Table of Contents  

Kodzo-Grey Venyo: A review of the literature on synovial sarcoma of the kidney

Introduction

Synovial cell sarcomas are tumours that contain a combination of histological features of both a carcinoma and a sarcoma. Synovial cell sarcomas may have epithelioid cells, mimicking carcinomas, that are intimately admixed with spindle cell sarcoma cells. In view of these features, pathologists have the task of differentiating between a poorly differentiated carcinoma and synovial cell sarcoma, which could potentially be an uphill task for the pathologist who has not previously encountered a case of synovial cell sarcoma. However, with the advent of immunohistochemistry, the pathologist can now confidently differentiate between a synovial cell carcinoma and a carcinoma. Synovial cell sarcomas have spindle cells that are positive for vimentin and epithelial components that are positive for cytokeratin (CK). Recently, in 2000,1,2 molecular diagnostic studies identified a unique translocation, t(X;18), fusing the SYT/SSX genes. Synovial cell sarcomas of the kidney are rare tumours, of which about 64 cases have been reported in the literature, and this paper reviews the literature on these tumours.

Literature review

Synovial sarcoma, which has also been referred to as synovioma, is a rare form of malignancy that usually occurs near the joints of the arm, neck or leg. It is one of the soft-tissue sarcomas3 and it has been stated that the terminology ‘synovial sarcoma’ was coined in the earlier part of the twentieth century when some researchers were of the opinion that the microscopic resemblance of some tumours to synovium, as well as its propensity to arise adjacent to joints, indicated a synovial origin; nevertheless, the actual cells from which the tumour develops are not known and perhaps not necessarily synovial.4

Primary synovial sarcomas are most commonly found in the soft tissues near the large joints of the arm and leg; however, they have also been found in most human tissues and organs including the intracranial sites/brain,5 heart,6 larynx,79 mediastinum,10 pleura,11 salivary gland,12 skin,13 thoracic region,14 back,15 prostate16,17 digestive tract18 and kidney.1921

It has been stated that synovial sarcoma occurs most commonly in the younger age group and represents approximately 8% of all soft-tissue sarcomas22 and approximately 15–20% of cases of soft-tissue sarcoma in adolescents and young adults.23 It has also been reported that the peak incidence of synovial sarcoma is before the age of 30 and that males are more frequently affected than females, with a ratio of 1.2:1.22

Histopathology

With regard to microscopic examination of synovial sarcomas, two histological cell types can be seen: (a) the fibrous type, which also known as the spindle or sarcomatous cell type (this type is relatively small and uniform and is found in sheets); and (b) the type with an epithelial appearance. Classical synovial sarcoma tends to have a biphasic appearance in which both cell types are present.24 It has also been reported that synovial sarcomas can be either poorly differentiated or monophasic fibrous, consisting only of sheets of spindle cells.24

It has been stated that, very rarely, there can be a monophasic epithelial form of synovial sarcoma that does cause some difficulty with regard to differential diagnosis.4

There is no universally agreed grading system for reporting the histopathology results of synovial sarcomas.25 According to Paul et al.,26 in Europe, the Trojani and French system of grading is becoming popular. However, the National Cancer Institute (NCI) grading system is more frequently used in the USA. Scoring of the sample using the Trojani system is dependent on the degree of tumour differentiation, mitotic index and tumour necrosis – between 0 and 6 – and the score then converts this into a grade between 1 and 3, with grade 1 representing a less aggressive tumour.25 The NCI system takes into consideration a number of other factors but also has three grades.

Molecular biology

With regard to molecular biology, most, if not all, synovial sarcomas are associated with the reciprocal translocation t(X;18)(p11.2;q11.2).24 There has been some debate among authors about whether or not this translocation is, by definition, indicative of synovial sarcoma.2729

According to Coindre et al.,30 the diagnosis of synovial sarcoma is typically made based on histology and is confirmed by the presence of t(X;18). This translocation event between the SS18 gene on chromosome 18 and one of three SSX genes (SSX1, SSX2 and SSX4) on chromosome X results in a SS18SSX fusion gene. The resulting fusion protein brings together the transcriptional activating domain of SS18 and the transcriptional repressor domains of SSX. SS18SSX is believed to underlie synovial sarcoma pathogenesis by causing dysregulation of gene expression.30

There is some association between the SS18SSX1 or SS18SSX2 fusion type and both tumour morphology and 5-year survival of patients with synovial sarcoma.31

Symptoms

It has been stated that synovial sarcomas usually tend to present as asymptomatic masses or swellings or they may, at times, present with general symptoms attributable to malignancies, such as fatigue.24

Treatment

Treatment of synovial sarcoma generally involves the following:

  1. Surgical excision to remove the tumour together with a surrounding safety margin of healthy tissue. Lewis et al.32 stated that this modality of treatment is the main synovial sarcoma treatment and is curative in about 20–70% of patients, depending on the particular study being quoted.

  2. Conventional chemotherapy (for example, the use of doxorubicin hydrochloride and ifosfamide) reduces the number of remaining microscopic cancer cells. It has been stated that the benefit of chemotherapy in synovial sarcoma to overall survival is not clear; however, a case report in 2004 revealed that survival of patients with advanced poorly differentiated disease marginally improves with doxorubicin/ifosfamide treatment.24,33

  3. Radiotherapy to reduce the chance of local recurrence. However, it has been stated that the benefit of radiotherapy in synovial sarcoma is less clear than the benefit for chemotherapy.24

Synovial cell sarcoma of the kidney

Synovial cell sarcoma of the kidney is an extremely rare entity which was first reported by Faria et al. in 1999.34 To the author’s knowledge, about 64 cases of synovial sarcoma of the kidney have so far been reported in the literature.

Synovial sarcoma usually involves adolescents and young adults although the age at presentation ranges from 17 to 61 years.20 The diagnosis of synovial sarcoma of the kidney is difficult because of its rarity and its similar presentation to other renal tumours. The differential diagnosis includes adult Wilms’ tumour, transitional cell carcinoma, renal cell carcinoma, haemangiopericytoma, congenital ectoblastic nephroma and primitive neuroectodermal tumour (PNET).20

Discussion

Zia et al.19 reported the case of a 35-year-old man who presented with sudden onset of right flank pain with haematuria. He was a non-smoker and his medical history was unremarkable but, on presentation, he was apyrexial with tenderness in the right lumbar region. Urine dipstick examination was positive for blood and protein and radiography of the abdomen was inconclusive. Computed tomography (CT) of the abdomen showed a large heterogeneous and well-defined mass measuring 15.4 cm × 13.8 cm × 9.5 cm. CT also revealed cystic and solid components arising from the right kidney and centred around the renal hilum with an anteroposterior extension abutting the psoas muscle posteriorly. Mild hydronephrosis was also uncovered, which involved the upper and lower poles of the right kidney, but no invasive features and no evidence of lymphadenopathy or intra-abdominal metastasis were found. He underwent a right nephrectomy and, during the procedure, one of his kidneys was found to be largely cystic. The cyst was ruptured during the operation and the kidney that was removed weighed 979 g and the largest specimen measured 15 cm × 10 cm × 7.5 cm. Macroscopic examination revealed that the kidney was largely occupied by partially solid and a partially cystic lesion with haemorrhagic and shiny grey, solid content. Microscopic examination of the tumour revealed monomorphic spindle cell proliferation taking the form of short intersecting fascicles or in solid sheets with high mitotic activity. There were also cysts of variable size, which were lined by inactive polygonal eosinophilic cells with apically located nuclei (hobnail appearance) within the tumour. Immunohistochemical examination of the tumour showed that the cells were positive for vimentin, Bcl-2 and CD99. The tumour cells were negative for desmin, smooth muscle actin (SMA), S100 protein, CD34, factor VIII, Melan A, CD117, leucocyte common antigen (LCA), epithelial membrane antigen (EMA), high-molecular-weight CK, CD10 and MyoD1. According to Zia et al.,19 appearances were consistent with biphasic synovial sarcoma with focal high-grade areas; subsequent cytogenetic analysis confirmed the diagnosis of synovial sarcoma, and reverse transcription polymerase chain reaction (RT-PCR) analysis showed SYT/SSX translocation, a characteristic feature of synovial sarcoma. The patient was treated with vincristine, ifosfamide, doxorubicin and etoposide chemotherapy, but no long-term follow-up was reported.

Dassi et al.20 reported the case of a 20-year-old woman with no associated history of haematuria or any other systemic symptoms but who presented with a mild left flank pain from which she had been suffering for a period of 1 week. Examination revealed a large non-tender lump in the left lumbar and left hypochondriac region. CT of the abdomen and pelvis showed a large heterogeneously enhancing mass measuring 14.3 cm × 9.4 cm × 8.5 cm over the mid-region and lower pole of the left kidney and showed areas of necrosis. An iso- to hypodense heterogeneously enhancing thrombus was noted in the left renal vein and adjacent portion of the inferior vena cava and a preoperative provisional diagnosis of renal cell carcinoma was made. The authors also reported a tumour that obscured the whole kidney during the patient’s operation. A left radical nephrectomy was performed and the left renal vein was ligated flush with the inferior vena cava after milking the thrombus into the left renal vein. The specimen was examined macroscopically and found to contain a tumour measuring 12.8 cm × 11 cm × 4.5 cm, obscuring the entire renal parenchyma, involving the pelvicalyceal system and medulla with a thin rim of cortex surrounding it. The tumour thrombus was seen within the lumen of the left renal vein and the authors also reported that microscopic examination of the tumour revealed that it was composed of spindle cells arranged in intersecting fascicles, alternating with hypocellular areas, suggestive of monophasic synovial sarcoma. Immunohistochemical examination of the tumour revealed that the cells expressed Bcl-2, calponin and EMA, and both MIC2 and CK were focally positive. Dassi et al.20 additionally reported that molecular analysis of the tumour revealed a translocation between the SYT gene and SSX on chromosome X, which was consistent with the diagnosis of synovial sarcoma. At the time of reporting, long-term follow-up outcome was not available and the authors concluded that they had described a case of primary synovial sarcoma of the kidney with caval thrombus in a young woman. This rare tumour is likely to be confused with other cell tumours of the kidney and the authors recommended that an accurate diagnosis, including cytogenetic and molecular studies, is imperative and primary synovial sarcoma should be included in the differential diagnosis of spindle cell tumours of the kidney.

Grampurohit et al.21 reported the case of a 21-year-old woman who presented with a history of fever, haematuria and right flank pain that had been ongoing for a period of 1 month. CT revealed a heterogeneous, soft-tissue mass with well-defined margins in the upper pole of the right kidney with solid, necrotic components and heterogeneous enhancement. There was no evidence of renal vein, inferior vena cava or atrial thrombosis, or local invasion or any lymphadenopathy. Based on the clinical and radiological findings, a provisional diagnosis of renal cell carcinoma was made. A right nephrectomy was performed and the nephrectomy specimen weighed 220 g and measured 12 cm × 6 cm × 3.5 cm. Macroscopic examination of the cut section of the specimen revealed a cystic tumour with soft, solid growth that was a yellow-tan colour in the upper pole and measured 4.5 cm × 4.4 cm × 4 cm. In addition, areas of haemorrhage and necrosis were seen. Histological examination of the specimen revealed a neoplasm that was composed of solid monomorphic sheets of round, plump cells showing a high nuclei to cytoplasmic ratio, clear-to-eosinophilic cytoplasm with central vesicular nuclei and prominent nucleoli. Within the stroma, there was rich vascularity with the vessels showing a haemangiopericytoma-like pattern. Five mitoses per 10 high-power field were noted and areas of necrosis and haemorrhage were also found. Multiple cortical scars and hyalinization were observed in the adjacent renal parenchyma. The tumour was seen to have extended into the renal calyces but there was no evidence of thrombosis in the ureter and renal vessel. Overall, the features were adjudged to be suggestive of malignant haemangiopericytoma. Grampurohit et al.21 reported that immunohistochemical study of the tumour showed strong positivity for Bcl-2, vimentin, CD99/MIC2, calponin and CD56, focal positivity for EMA and CK (Figure 1) and negativity for muscle-specific desmin, actin, CD117, CD34 and CD31. The authors reported that the morphological and immunohistochemical features were compatible with the diagnosis of poorly differentiated synovial sarcoma (PDSS) of the kidney. They also stated that, postoperatively, the patient was free of local recurrence or metastasis 6 months following the nephrectomy. No long-term follow-up in this case was reported, so the long-term outcome is not known.

FIGURE 1

Chest CT scan shows haematogenous dissemination of variable size, multiple nodular opacities with vascular connection in the entire lobe of the right lung. Reprinted with permission from Park SJ, Kim HK, Kim CK, et al. A case of renal synovial sarcoma: complete remission was induced by chemotherapy with doxorubicin and ifosfamide. Korean J Intern Med 2004; 19:62–5.33

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According to Skytting et al.,35 primary synovial sarcoma occurs in two forms, biphasic and monophasic, and primary biphasic synovial sarcoma contains both glandular elements and spindle epithelial cells, whereas the primary monophasic synovial sarcomas are composed of spindle cells only. Skytting et al.35 reported that monophasic synovial sarcoma is difficult to diagnose solely on histological examination and, therefore, molecular analysis is required to confirm the diagnosis. In addition, the characteristic chromosomal translocation seen in synovial sarcoma is t(X;18)(p11.2;q11.2). This translocation leads to fusion of the SYT gene located on chromosome 18 with the SSX gene located on chromosome X. According to the authors, five variants of the SSX gene have been identified but only SSX1 and SSX2 have been shown to fuse with the SYT gene. To the knowledge of the author, about four cases of synovial sarcoma with caval thrombus have been reported.

Tornkvist et al.36 reported a case of metastatic disease due to synovial sarcoma. The patient underwent a right nephrectomy as there was a large tumour in the right kidney. The histological diagnosis of the tumour was haemangiopericytoma and, less than 1 year later, another operation was necessary to eliminate local recurrence. The histological examination revealed poorly differentiated tumour tissue with haemangiopericytoma-like features. Immunohistochemical staining showed immunoreactivity to CK, EMA and vimentin, but the tumour was negative for CD34 and factor VIII. The tumour cell proliferation, assessed by Ki67, was high and RT-PCR analysis and sequence analysis demonstrated the presence of the SS18/SSX2 tumour gene. Histological review of the tumour specimen confirmed haemangiopericytoma-like morphology. The final diagnosis was PDSS and, at the time of reoperation, lung metastases had detected via radiography, indicating that the tumour was highly aggressive. Tornkvist et al.36 stated that:

  • To their knowledge, their case was the third case of PDSS.

  • The haemangiopericytoma-like histology and a very aggressive clinical behaviour were common to all three cases.

  • These circumstances accentuate the impact of SS18/SSX in the analysis of haemangiopericytoma-like tumours.

Dassi et al.20 stipulated that there are no agreed established guidelines regarding the management of synovial sarcoma of the kidney in view of the limited number of reported cases. They also stated that primary surgical treatment is considered to be the treatment of choice; however, the prognosis is poor with this treatment modality alone and the value of chemotherapy is yet to be proven, but synovial sarcoma may be sensitive to high doses of ifosamide- and doxorubicin-based regimens.

Park et al.33 reported complete remission of metastatic lung lesions when using ifosamide and doxorubicin during a 4-week course of treatment. The authors reported the case of a 32-year-old woman who presented with intermittent abdominal pain. Abdominal ultrasonography showed a well-defined echogenic mass on the left kidney; therefore, she underwent CT, which showed a well-defined mass with heterogeneous enhancement in the lower pole of the left kidney with hilar infiltration, measuring 12 cm × 10 cm in size (Figure 2), and small hilar lymph nodes and a thrombus were observed in the left renal vein. Left radical nephrectomy with left renal vein thrombectomy and macroscopic examination revealed a 13 cm × 12 cm × 11 cm mass in the lower pole of the left kidney. The cut surface of the mass was greyish-white mixed with focal necrosis and haemorrhage (Figure 3). Microscopic examination of the specimen revealed a highly cellular tumour composed of mitotically active (up to 30 mitoses per high-power field), atypical plump spindle cells and indistinct cell borders arranged in short and intersecting fascicles, mainly involving the renal pelvis with extension to the renal cortex and capsule (Figure 4). Malignant cells were not seen in the dissected lymph nodes or renal vein. Immunohistochemical staining revealed that the tumour stained positive with vimentin (Figure 5), but negative for CK, EMA, S100 and CD34. There were no extrarenal manifestations and a diagnosis of left renal spindle cell-type monophasic synovial sarcoma was made. Four months later, chest radiography and CT of the chest revealed variable sized nodular opacities with vascular connections in the entire in the entire lobe of the left lung (see Figure 1). The patient then underwent a percutaneous transthoracic biopsy of the right lower lung nodule, and histological examination of the biopsy was consistent with synovial sarcoma (Figure 6). She had combination chemotherapy with 28-day cycles of 2500 mg/m2 ifosfamide on days 1–3, plus 60 mg/m2 doxorubicin on day 1. Following the second cycle of chemotherapy, follow-up CT of the chest showed smaller nodules on the right lung and the patient was declared to be in partial remission. During the chemotherapy, the patient developed grade 2 neutropenia and grade 1 thrombocytopenia as well as non-haematological toxicities such as nausea and alopecia. She received all the planned doses of chemotherapy without dose reduction and complete remission was achieved once she had received six cycles of chemotherapy (Figure 7). The experience of Park et al.33 in treating their patient would indicate that synovial sarcoma of the kidney responds to chemotherapy.

FIGURE 2

Computed tomography scan showing a 12 cm × 10 cm well-defined mass on the lower pole of the left kidney. The mass shows heterogeneous enhancement. Reprinted with permission from Park SJ, Kim HK, Kim CK, et al. A case of renal synovial sarcoma: complete remission was induced by chemotherapy with doxorubicin and ifosfamide. Korean J Intern Med 2004; 19:62–5.33

7-1-2-fig2.jpg
FIGURE 3

The cut surface of the mass shows greyish-white tissue mixed with focal necrosis and haemorrhage. Reprinted with permission from Park SJ, Kim HK, Kim CK, et al. A case of renal synovial sarcoma: complete remission was induced by chemotherapy with doxorubicin and ifosfamide. Korean J Intern Med 2004; 19:62–5.33

7-1-2-fig3.jpg
FIGURE 4

A microscopic study revealed a highly cellular tumour composed of mitotically active, atypical plump spindle cells and indistinct cell borders arranged in short, intersecting fascicles. Haematoxylin and eosin staining, ×200 magnification. Reprinted with permission from Park SJ, Kim HK, Kim CK, et al. A case of renal synovial sarcoma: complete remission was induced by chemotherapy with doxorubicin and ifosfamide. Korean J Intern Med 2004; 19:62–5.33

7-1-2-fig4.jpg
FIGURE 5

Immunostaining for vimentin shows positive reaction. Magnification ×20. Reprinted with permission from Park SJ, Kim HK, Kim CK, et al. A case of renal synovial sarcoma: complete remission was induced by chemotherapy with doxorubicin and ifosfamide. Korean J Intern Med 2004; 19:62–5.33

7-1-2-fig5.jpg
FIGURE 6

Microscopic examination of percutaneous transthoracic needle biopsy of lung nodule shows plump spindle cells, which are consistent with renal synovial sarcoma. Haematoxylin and eosin staining, ×200 magnification. Reprinted with permission from Park SJ, Kim HK, Kim CK, et al. A case of renal synovial sarcoma: complete remission was induced by chemotherapy with doxorubicin and ifosfamide. Korean J Intern Med 2004; 19:62–5.33

7-1-2-fig6.jpg
FIGURE 7

Follow-up CT scan of the chest shows complete disappearance of nodular opacities after six cycles of chemotherapy. Reprinted with permission from Park SJ, Kim HK, Kim CK, et al. A case of renal synovial sarcoma: complete remission was induced by chemotherapy with doxorubicin and ifosfamide. Korean J Intern Med 2004; 19:62–5.33

7-1-2-fig7.jpg

Some authors3638 consider that synovial sarcoma is histologically subclassified into biphasic spindle cell, monophasic spindle cell and poorly differentiated variants. PDSSs constitute about 20% of cases and are associated with the poorest prognosis. According to the same authors,3638 PDSSs exhibit three histological variants: large cell, small cell and high-grade spindle cell variants. In addition, PDSS is composed of sheets of undifferentiated round cells with hyperchromatic nuclei and frequent mitoses and such tumours are often associated with a rich vascular pattern comprising dilated, thin-walled vascular spaces that resemble haemangiopericytoma.

Grampurohit et al.21 reported that primary renal sarcomas are rare tumours and account for 1% of malignant renal tumours. The most frequent type is leiomyosarcoma, constituting 40–60%, followed by rhabdomyosarcoma, chondrosarcoma, osteosarcoma, liposarcoma, angiosarcoma and haemangiopericytoma. Grampurohit et al.21 found 25 cases of monophasic spindle cell synovial sarcoma, two cases of biphasic synovial sarcomas and seven cases of PDSSs in the kidney in the literature and reported that their case was the eighth documented case of the poorly differentiated variant.

Some authors20,39 believe that there is no clinical or imaging characteristic that enables a diagnosis of synovial sarcoma of the kidney.20,39 According to others,1,37,40 radiographic and gross examination in most cases of synovial sarcomas of the kidney leads to a diagnosis of renal cell carcinoma. The tumours are generally well-defined, irregular large masses ranging in size from 5 to 20 cm. Grossly identifiable smooth-walled cysts were found in eight cases while the case reported by Grampurohit et al.21 also had a cystic component. Tornkvist et al.36 reported that a subset of PDSSs display haemangiopericytoma-like morphology and many have been misdiagnosed as haemangiopericytoma.

A number of authors1,2,20,3642 have reported immunophenotypical overlap among three tumour entities, PDSS, PNET and malignant peripheral nerve sheath tumour. These three tumour types may be differentiated by the use of a panel of antibodies. Immunohistochemistry for primary synovial sarcomas of the kidney consistently reveals positivity for Bcl-2, CD99/MIC2, CD56 and vimentin and focal positivity for EMA; however, they do not stain for desmin, actin, CD34 and CD31. Although EMA is not a specific marker of synovial sarcoma, its presence in poorly differentiated sarcoma can suggest synovial sarcoma.42 The simultaneous use of antibodies to both CD99 and CD56 may be helpful in the differential diagnosis of PDSS as synovial sarcoma will almost invariably be positive with both;42 however, PNETs will be CD99 positive and CD56 negative, and malignant peripheral nerve sheath tumours will be CD99 negative and CD56 positive.

It is generally1,2,3644 agreed that the diagnosis of synovial sarcoma can be confirmed by RT-PCR analysis, which reveals a unique chromosomal translocation, t(X;18)(p11.2;q11.2), resulting in the fusion of the SYT gene on chromosome 18 with the SSX family gene on chromosome X.

The differential diagnosis of synovial sarcoma of the kidney includes Wilms’ tumour, mixed epithelial and stromal tumours, sarcomatous renal cell carcinoma, congenital ectoblastic nephroma, PNET, malignant peripheral nerve sheath tumour and haemangiopericytoma.3638,44 To establish a diagnosis of renal synovial sarcoma, it is also be necessary to rule out the distant metastases and secondary extension of retroperitoneal synovial sarcoma. Haemangiopericytoma can be differentiated from synovial sarcoma because haemangiopericytoma is CD34 positive and CK negative.

Dassi et al.20 and Schaal et al.39 consider primary surgical resection the treatment modality of choice for synovial sarcoma, but the outcome is poor with this treatment alone. Synovial sarcomas may be sensitive to high-dose ifosfamide- and adriamycin-based regimens.

As the number of cases of synovial sarcoma of the kidney is small owing to its rarity, no clear medical guidelines have been established.43

Gabilondo et al.44 reported the case of a 32-year-old woman with primary synovial sarcoma of the kidney. The diagnosis was corroborated by in situ PCR, which showed chromosomal translocation t(X;18)(p11.2;q11.2) in tissue homogenate. Gabilondo et al.44 stated that synovial sarcoma of the kidney may be confused with other spindle cell tumours and, for that reason, in situ PCR may be useful to confirm the diagnosis in paraffin-embedded material.

Jun et al.45 reported three cases of synovial sarcoma with rhabdoid features that were initially diagnosed as adult rhabdoid tumours. Of the three patients, two were women aged 35 and 27 years and the third was a man aged 26 years. All three patients presented to their physicians with right flank pain. Jun et al.45 also reported that, on physical examination, they found a poorly defined, firm, palpable mass in the upper right quadrant of the abdomen in all three cases. Ultrasonography and CT revealed solid, cystic masses in the right kidneys, which ranged in size from 8.5 cm to 29.0 cm; therefore, right radical nephrectomies were performed in all the three patients. One patient died from the disease and the remaining two patients were alive and disease free after chemotherapy and radiotherapy. Jun et al.45 also reported that microscopic examination of the tumours revealed that the tumours were composed mostly of rhabdoid cells with eccentrically located nuclei, prominent nucleoli and eosinophilic cytoplasm. They also found areas of fasciculate spindle cells, sharply separated from, or irregularly admixed with, areas of rhabdoid cells. There was evidence of tumour necrosis but no epithelial areas were seen. They also observed haemangiopericytic vasculature, at least focally, in all the cases. With regard to immmunohistochemistry, the tumour cells were positive for CD99 and Bcl-2 in all cases and for CD56 in two cases and negative for CD34 and SMA in all cases. The cells in one of the cases were focally positive for CK and, in order to verify the possibility of synovial sarcoma with rhabdoid features, the authors performed RT-PCR using RNA extracted from frozen tissue that was formalin fixed in the first case and from paraffin-embedded tissue in the other two cases. SYTSSX2 transcripts were detected in all the three cases and the authors believed that these cases indicated that synovial sarcoma of the kidney should be considered in the differential diagnosis of mesenchymal kidney tumours with prominent rhabdoid features. They also stated that a subset of adult rhabdoid tumours may be a rhabdoid variant of synovial sarcoma and, for an accurate diagnosis, they would recommend molecular studies to detect SYTSSX fusion transcripts.45

Argani et al.1 reported 15 primary renal neoplasms with morphological, immunohistochemical and molecular features identical to those of synovial sarcoma. They considered that these tumours constitute a subset of the entity that was previously designated embryonic sarcoma of the kidney. Most patients with these tumours were diagnosed between the ages of 20 and 50 years. In addition, the tumours were large, partially necrotic and usually contained smooth-walled cysts on gross examination. They also reported that on microscopic examination, the tumours were characterized by mitotically active, monomorphic plump spindle cells with indistinct cell borders growing in short intersecting fascicles. The grossly identified cysts were lined by mitotically inactive polygonal eosinophilic cells with apically oriented nuclei (‘hobnailed epithelium’). The results of immunohistochemistry showed that the spindle cells were immunoreactive for vimentin, often immunoreactive for EMA, but typically non-immunoreactive for desmin, actin, S100, and CK, whereas the cyst epithelium was CK positive. These findings were consistent with monophasic, spindled synovial sarcoma encircling dilated native renal collecting ducts. The authors also reported that the presence of a SYTSSX gene fusion resulting from the t(X;18) characteristic of synovial sarcoma was demonstrated by RT-PCR in all of the tumours for which adequate RNA was obtained from paraffin blocks. An additional case demonstrated the characteristic t(X;18) translocation on cytogenetic analysis, but adequate material to perform molecular studies was not available in this case or the remaining 11 cases. Argani et al.1 concluded that primary renal synovial sarcoma is a rare distinctive clinicopathological entity confirmed by the molecular detection of the SYTSSX fusion transcript.

Kim et al.2 reported two cases of primary synovial sarcoma of the kidney. Both patients had a mass in the upper part of the right kidney without any primary extrarenal neoplastic lesions. Macroscopic examination of the tumours revealed that both were soft or rubbery masses measuring 5.5 cm and 5 cm in diameter. Microscopic examination of the tumours revealed that both tumours were PDSSs and the lesions had a hypercellular solid or lobular growth of round, oval or short spindle cells in variably solid sheets, in intersecting fascicles, or in a haphazard fashion. Areas of solid aggregation or fascicles of the tumour cells alternating with hypocellular myxoid tissues with areas displaying a prominent haemangiopericytoma-like pattern were found. Immunohistochemical studies revealed that vimentin was diffusely positive and a few tumour cells were positive for CK, EMA and neurofilament. The tumour cells were negative for S100, CD34, SMA and desmin, but were CD56 and CD99 positive. The authors reported RT-PCR in both cases using formalin-fixed, paraffin-embedded tissues detected SYTSSX2 fusion gene transcripts, which are characteristic molecular findings of synovial sarcoma. One of the two patients died 10 months after the diagnosis of synovial sarcoma of the kidney and the authors concluded that these tumours are unique cases of primary synovial sarcoma of the kidney confirmed by molecular study.

According to Srinivas et al.,46 sarcoma originating in kidneys of adults is rare and leiomyosarcoma is the most common renal sarcoma, accounting for 40–60% of such tumours, followed by rhabdomyosarcoma, angiosarcoma, haemangiopericytoma, liposarcoma, chondrosarcoma and osteosarcoma. Gonzalez Crussi and Baum47 stated that sarcoma of the kidney in childhood is mainly confined to clear cell sarcoma of the kidney and malignant rhabdoid tumour.

Ezinger and Weis48 stated that synovial sarcoma is the fourth most common sarcoma as it accounts for 5–10% of all soft tissue sarcoma cases. Fisher49 listed the unusual sites of synovial sarcoma as head and neck, face, tonsil, larynx, trachea, intracranial, third ventricle, abdominal wall, vulva, intra-abdominal, mesentery, retroperitoneal space, chest wall, intrathoracic, pleura, lung, mediastinum, heart, oesophagus, intraosseous, intravascular and intramural.

Fisher49 summarized the immunohistochemical staining characteristics of biphasic and monophasic synovial sarcomas for the various markers and their percentage positivity rates as:

  • Cytokeratin – 100%, 68% and 81% for biphasic sarcoma, monophasic sarcoma and all forms, respectively.

  • Epithelial membrane antigen – 100%, 73% and 84% for the biphasic, monophasic and all forms, respectively.

  • Carcinoembryonic antigen – 37%, 8% and 20% for the biphasic, monophasic and all forms, respectively.

  • LEU7 – 50%, 33% and 40% for the biphasic, monophasic and all forms, respectively.

  • S100 – 42%, 27% and 30% for the biphasic, monophasic and all forms, respectively.

  • CD99 – 67%, 61% and 62% respectively for the biphasic, monophasic and all forms, respectively.

  • Bcl-2 – 100%, 100% and 100% respectively for the biphasic, monophasic and all forms, respectively.

Spillane et al.50 reported that synovial sarcomas are chemosensitive to ifosfamide- and doxorubicin-based chemotherapy with a response rate of 24%. Kawai et al.51 stated that the prognosis of renal synovial sarcoma, despite treatment, is poor with a 5-year survival rate of between 42% and 89%. Trassard et al.52 listed the factors that predict worse prognosis for patients with synovial sarcoma as tumour size > 5 cm, being male, older age (> 20 years), extensive tumour necrosis, high grade, large number of mitotic figures (> 10 per 10 high-power fields), neurovascular invasion and the SYTSSX1 variant.

Iacovelli et al.53 were the first to describe the clinical characteristics of primary renal synovial sarcoma and examined the association of histological features with the expression of immunohistological markers. The authors collated published data on all cases of primary synovial sarcoma of the kidney, from its first description in 1999 to September 2011. They extracted data on clinical and pathological characteristics of the renal synovial sarcomas, which they used to create a database. They estimated the disease-free survival and overall survival rates by using the Kaplan–Meier method with Rothman’s 95% confidence intervals (CIs) and they compared rates across the groups using a log-rank test. They evaluated the association between tumour extension and histological features using the non-parametric Spearman’s rank-order correlation test and used a chi-squared test to assess the differences between the groups. The authors reported that, in the cohort overall, the median overall survival was 48 months (95% CI 14.1–81.9 months) and Cox analysis revealed that the risk of death at diagnosis was greatly increased in patients with metastatic disease compared with those with non-metastatic disease (hazard ratio 343.9, 95% CI 2.8 to 42 000; P = 0.017). The median disease-free survival was 33.0 months (95% CI 16.8–49.2 months) and the patients who developed metastatic disease had a very poor prognosis with a median survival of 6 months (95% CI 5.1–6.9 months). The observed microscopic features were monophonic, biphasic and PDSS in 76%, 16% and 8% of patients, respectively. Iacovelli et al.53 found significant differences in the expression of immunohistochemical markers or genetic mutation between the different subtypes of renal synovial sarcomas. They also reported that the risk of relapse for patients with non-metastatic disease at diagnosis was 36%. Iacovelli et al.53 concluded that:

  • Despite the retrospective nature of their study, the results showed that renal synovial sarcoma comprises different histological subtypes, which are characterized by specific immunohistochemical stains and by specific translocations.

  • When diagnosed at the metastatic stage, the prognosis was very poor in comparison with that for non-metastatic disease; however, one out of three patients with non-metastatic disease experienced disease relapse.

The authors recommended that cooperative efforts and publication of cases with adequate follow-up are necessary to better define prognosis and therapeutic strategies for this rare disease.

Perlmutter et al.54 reported the case of a 61-year-old woman who presented with right loin pain and visible haematuria. Magnetic resonance imaging (MRI), revealed a heterogeneous enhancing soft-tissue density in the upper pole of the right kidney and extending into the renal pelvis. The mass had a cystic appearance with irregular septations and a peripheral nodule measuring 7.0 mm in diameter. There was no evidence of extracapsular extension or venous involvement and the patient subsequently underwent right ureteroscopy and biopsy of the renal mass and the pathology report revealed the presence of atypical cells, but it was otherwise non-diagnostic. The patient then underwent a right nephroureterectomy with the working diagnosis of transitional cell carcinoma of the kidney. The intraoperative frozen section report was read as low-grade transitional cell carcinoma of the kidney. The excised tumour appeared grossly irregular in shape, invaded the upper pole calyces and renal pelvis without capsular penetration and measured 4 cm × 2.5 cm × 2.5 cm. Many dark-red haemorrhagic centres were present and the hilar lymph nodes and the renal vessels were free from tumour invasion. Microscopic examination revealed that the tumour exhibited a monophasic growth pattern and portions of the tumour contained cysts of various sizes lined by a single layer of epithelial cells with eosinophilic cytoplasm and apical nuclei giving the classic hobnail appearance. The intervening stroma was cellular and primitive in nature. Mitotically active spindle cells that grew in an expansile fashion were the predominant stromal component. The poorly differentiated neoplastic cells stained positively for CD56, Wilms’ tumour 1 (WT1), vimentin, E-cadherin and neuron-specific enolase. There was no uptake of stains for actin, CD15 and desmin. The initial diagnosis was nephroblastoma (Wilms’ tumour) with a diffuse blastema pattern. The slides were examined by another pathologist for a second opinion. The second pathologist undertook further immunohistochemical staining, which was unequivocally positive for EMA. Oestrogen receptors were negative for both epithelial and spindle cell components, but progesterone receptors were positive for spindle cells. The diagnosis of the second pathologist was primary renal synovial sarcoma and the diagnosis was confirmed by means of PCR to detect SYTSSX fusion. The patient was offered adjuvant chemotherapy, which she refused, but she was alive and disease-free 5 months after her nephroureterectomy operation.

Wang et al.55 reported the case of a 31-year-old man who presented with visible haematuria and right flank pain. Ultrasonography of the renal tract revealed a low-echogenic mass in the right kidney. CT of the abdomen and pelvis revealed a 7.0 cm × 6.6 cm contrast-enhancing mass in the lower pole of the right kidney. There was no evidence of any lymph node involvement, vascular invasion or metastasis. Chest radiography was normal and a right nephrectomy was undertaken. Gross examination of the specimen revealed a 7 cm × 7 cm × 4 cm tumour and the cut surface of the mass was tawny in colour and firm with focal haemorrhage and necrosis. The renal capsule had not been invaded and histological examination of the specimen revealed that the tumour was composed of mitotically active, monomorphic plump spindle cells with indistinct cell borders. Immunohistochemical studies showed that the tumour cells were positive for CD99, EMA and Ki67, but negative for WT1, desmin, PCK, LCA, S100, CK7, CK20, CD10 and CD34. Fluorescence in situ hybridization (FISH) was utilized to detect SSYSSX fusion transcript product by the t(X;18)(p11.2;q11.2) using RNA extracted from paraffin blocks. The case was positive for SSX18 group translocation. The patient underwent chemotherapy for 1 month and combination chemotherapy with 24-day cycles of 80 mg pirarubicin on day 1 and 500 mg dacarbazine on days 1–3. He received a total of four cycles of treatment and remained well without any evidence of recurrence for 9 months, with regular follow-ups scheduled.

Wang et al.56 demonstrated the clinicopathological and immunohistochemical features, differential diagnoses and prognosis of synovial sarcomas of the kidney. The authors reviewed the histology slides and clinical data of four patients who had synovial sarcoma of the kidney and for whom immunohistochemical studies were carried out. Molecular analysis was performed in two cases to demonstrate the presence of the SSYSSX gene fusion transcripts by RT-PCR. Wang et al.56 reported that:

  • The patients were aged between 32 and 48 years and had a 1:1 ratio of men to women.

  • The tumours were 10.0 to 15.0 cm in diameter, grey-white in colour and solid, and haemorrhage and necrosis were observed.

  • Microscopically, the tumours consisted of mitotically active, monomorphic plump spindle cells with indistinct cell borders growing in intersecting fascicles. Hypocellular myxoid areas and a prominent haemangiopericytomatous pattern were present in all cases.

  • The average mitotic rate was 5–8 mitoses per 10 high-power fields.

  • Haemorrhage and tumour necrosis were easily identified.

  • Scattered small cysts lined with flat cuboidal, or hobnailed, epithelia were observed in three cases.

  • The tumour cells were immunoreactive for vimentin (all cases), Bcl-2 (all cases), CD99 (all cases), CD56 (three out of four cases), and focally for EMA (three out of four cases) and CK (three out of four cases). The SYTSSX1 gene fusion was detected in the two cases in which RT-PCR analysis was undertaken.

  • One patient suffered from tumour metastasis to the lung 6 months after surgery and died 5 months later. Multiple metastases to the liver occurred in one patient who died 13 months after the initial surgery and the remaining two patients suffered tumour recurrence at 8 months and 15 months and died at 18 months and 21 months, respectively, after the initial operation.

Wang et al.56 iterated that primary renal synovial sarcoma is rare, has a poor prognosis, is characterized by SYTSSX gene fusion and needs to be differentiated from other renal sarcomas.

Gulum et al.57 reported two cases of primary renal synovial sarcoma that were treated successfully by radical nephrectomy as detailed below.

Case 1

An 18-year-old woman presented with right flank pain and underwent ultrasonography of renal tract, which revealed a 7 cm mass in the mid-pole of the left kidney. She then underwent CT of the abdomen, which confirmed a 7 cm × 7 cm × 6 cm low-density mass in the mid-pole of the left kidney. A transitional cell carcinoma affecting the left kidney was suspected and, thus, left nephroureterectomy was performed. There was no evidence of involvement of the surrounding tissue or regional lymph nodes, histological examination of the tumour revealed solid cellular islets and there was no extracapsular extension of the tumour. The examination showed tumour tissues composed of solid cellular conglomerates of monomorphic spindle cells with non-uniformly bounded cytoplasm in large areas and fascicles with cystic structures settled among them. Immunohistochemical staining of the tumour was reported as:

  1. The epithelial cells were focally positive for Bcl-2 and CD99, and positive for CK, EMA and vimentin.

  2. The spindle cells were negative for Bcl-2, CK, EMA and CD99, and positive for vimentin.

Chemotherapy was recommended but the patient refused; however, she remained well and there was no evidence of recurrence of tumour at a 15-month follow-up.

Case 2

A 66-year-old woman presented with a 3-month history of abdominal distension and right flank pain. MRI revealed a heterogeneous enhancing soft-tissue mass originating from the upper pole of the right kidney and exhibited a distinct press on the inferior vena cava and repelled the renovascular structures and aorta. The mass consisted of cystic necrotic structures in a patchy manner and had a capsule. There was no evidence of extracapsular extension seen on the scan. The patient then underwent right nephroureterectomy and the tumour was found to be approximately 20 cm, originating from upper pole of the right kidney, which was stuck to the inferior vena cava. The resected tumour was irregular in shape and measured 25 cm × 15 cm × 7 cm. There was an infiltrative growth pattern to the tissue surrounding the kidney and the cut surface of the mass was greyish-white in colour and showed focal haemorrhage and yellow-grey necrosis. Histological examination of the tumour revealed solid cellular conglomerates of monomorphic spindle cells with non-uniformly bounded cytoplasm in large areas and fascicles with cystic structures settled among them. Immunohistochemical staining of the tumour was reported as:

  1. The epithelial cells were focally positive for Bcl-2 and CD99, and stained positively for CK, EMA and vimentin.

  2. The spindle cells were negative for Bcl-2, CK and CD99, focally positive for EMA, and positive for vimentin.

The patient underwent three cycles of ifosfamide, mesna and doxorubicin (IMA) chemotherapy. A dose of 60 mg/m2 (70 mg) doxorubicin was given on the first day only, 2500 mg/m2 (3000 mg) ifosfamide was given for 1–3 days and 2500 mg/m2 (3000 mg) mesna for 1–3 days. The patient had no evidence of recurrence at an 11-month follow-up.

Ozkan et al.58 reported the case of a 69-year-old woman who presented with a 1-month history of abdominal distension and right flank pain. MRI revealed a heterogeneous enhancing soft-tissue mass originating from the upper pole of the right kidney and exerting distinct pressure on the inferior vena cava, shifting the renovascular structures and aorta. The mass consisted of cystic necrotic structures that were situated in a patchy manner and had a capsule; however, no extracapsular extension was found. The patient underwent right nephroureterectomy and the tumour was found to be about 20 cm intraoperatively and originated from the upper pole of the right kidney and was adherent to the inferior vena cava. The excised tumour appeared irregular in shape and measured 25 cm × 15 cm × 7 cm. It showed infiltrative growth into the surrounding renal tissue and the cut surface of the mass was greyish-white in colour and had areas of focal haemorrhage and yellow-grey necrosis. Histological examination of the tumour revealed solid cellular conglomerates of monomorphic spindle cells with non-uniformly bound cytoplasm in large areas and fascicles with cystic structures settled among them. The active mitotic figures in the tumour totalled a median of 7 per 10 high-power magnification fields and the tumour exhibited necrotic and haemorrhagic areas. The inner surface of the cystic structures was lined with epithelial cells with large eosinophilic cytoplasm and apically located nuclei, which showed a classical hobnail appearance. On immunohistochemical staining, the tumour cells stained positive for vimentin and Bcl-2, and focally for CD99 and EMA. However, there was no uptake for pan-CK, actin, desmin, CD10 or low-molecular weight CK. A diagnosis of synovial sarcoma of the kidney was made and the patient underwent four courses of IMA chemotherapy, each of which was given in 3 days [a dose of 60 mg/m2 (70  mg) doxorubicin was given on the first day only, 2500 mg/m2 (3000 mg) ifosfamide was given for 1–3 days and 2500 mg/m2 (3000 mg) mesna for 1–3 days]. The control CT scans showed no evidence of recurrence after the third course of treatment.

Kawahara et al.43 reported the case of a 40-year-old woman who saw her local doctor because of right-sided abdominal pain. Abdominal CT revealed a tumour in the right kidney measuring 10 cm in diameter. Based on the CT findings, the possibility of angiomyolipoma could not be ruled out, but a high maximum standard uptake value of 7.8 was observed on a positron emission tomography CT scan and the possibility of malignancy was reported. The patient then underwent a transperitoneal right radical nephrectomy and the tumour was found to account for a large proportion of the excised kidney. The surrounding areas had taken on a cyst-like structure and the interior comprised greyish brittle tissue exhibiting solid growth. Histologically, gland- and cyst-like structures composed of cylindrical cuboidal cells and mainly characterized by the solid growth of short fusiform and oval-shaped basophilic cells were observed. Immunohistochemical staining of the tumour revealed partial positive staining for Bcl-2, MIC2, vimentin and AE1/AE3, while S100, WT1and SMA were negative. Furthermore, the SYTSSX fusion gene was positive in a PCR test. Based on these results, the patient was diagnosed with synovial sarcoma of the kidney; however, there was no follow-up information for this patient.

Park et al.40 reported the case of a 35-year-old woman who underwent a left radical nephrectomy for a mass in the lower pole of her left kidney that was found by chance during ultrasonography of her abdomen and renal tract. Macroscopic examination of the tumour revealed a homogeneously tan-coloured soft mass measuring 4.5 cm × 3.2 cm × 3.0 cm and circumscribed by a well-defined cystic space. The lesion exhibited hypercellularity of the oval or short spindle cells that were arranged in various solid sheets of intersecting fascicles. Immunohistochemical staining of the tumour revealed that it showed diffuse positivity for vimentin, Bcl-2 and CD99, and focal positivity for EMA. The SYTSSX fusion transcripts were detected by RT-PCR.

Zhao et al.59 reported the case of a 44-year-old woman who underwent left laparoscopic nephrectomy for a 6-cm renal mass. Intraoperatively, she decompensated into pulseless electrical activity from multiple pulmonary emboli secondary to a dislodged tumour thrombus that required emergency sternotomy and embolectomy after placing the patient on a cardiopulmonary bypass. She survived the surgery and was placed on adriamycin, ifosfomide and mesna chemotherapy. Histological examination of the tumour revealed primary monophasic synovial sarcoma of the kidney and molecular studies detected SYTSSX2 fusion transcripts consistent with t(X,18) translocation. Repeat CT of the chest revealed a non-occlusive filing defect at the bifurcation of the main pulmonary artery suggesting in situ thrombus, as well as new lytic osseous lesions in the intervertebral bodies, which were suspected to cause osseous metastasis.

Nishida et al.60 reported the case of a 63-year-old woman who presented with dysuria and visible haematuria. The results of cystoscopy were normal results and subsequent ultrasonography showed a complex renal mass of 5 cm at its greatest dimension. CT revealed a 5 cm complex cystic mass containing mildly thickened septation as well as a slightly contrast-enhancing region. There was no evidence of calcification or capsular involvement by the tumour and MRI allowed the solid components of the tumour to be visualized. The tumour was found in the upper pole of the kidney and a preoperative diagnosis of renal cell carcinoma cT1cN0cM0c was made. The patient underwent a radical nephrectomy and macroscopic examination revealed that the lateral side of the upper pole of the kidney had been replaced by a multiloculated cystic mass accompanied with a solid component. A massive haematoma, formed from intraoperative bleeding, was seen between the kidney and the extrarenal connective tissue. Microscopic examination revealed spindle cells with dark-staining nuclei and indistinct cytoplasm proliferated densely in the solid component. Spindle cells were arranged in bundle, fascicular or storiform pattern. Immunohistochemical studies of the tumour revealed that vimentin was positive for both spindle cells of the solid component and epithelial cells lining cysts and CD99, CD56, Bcl-2 and focal cytoplasmic staining for c-Kit were positive in spindle cells but negative in epithelial cells. Pan-CK, CK7, CD10 and beta-2-microglobulin were positive in epithelial cells but negative in spindle cells. Nishida et al.60 stated that, given these findings, the cysts were thought to be entrapped dilated renal tubules, but not an epithelial component of biphasic synovial sarcoma and, therefore, monophasic synovial sarcoma was suspected. The results of FISH analysis using a break-apart style probe were consistent with synovial sarcoma. The patient was alive and free of recurrence at a 1-year follow-up.

Zakhary et al.61 reported the case of a 52-year-old woman who presented with right flank pain. CT examination revealed an amorphous and partially cystic right lower pole renal mass with heterogeneous enhancement. Subsequent MRI revealed a 6.0 cm × 5.9 cm × 6.1 cm mass in the lower pole of the right kidney. The mass was reported to be heterogeneous, with the posterior region having similar intensity to skeletal muscle and the anterior region having higher signal intensity. On chemical shift imaging, the tumour showed no areas of signal intensity loss; axial T2-weighted images revealed marked heterogeneity with areas of high, intermediate and low signal, known as the ‘triple sign’. Based on these findings, the radiologists diagnosed renal cell carcinoma. The patient underwent a right radical nephrectomy with a pathological diagnosis of high-grade and poorly differentiated spindle cell synovial sarcoma. Immunohistochemical staining revealed focal positivity for CK (CAM 5.2) and negativity for S100 and EMA. Based on these findings, a diagnosis of primary synovial sarcoma of the kidney was given and the case was reported without any follow-up report on the patient’s progress.

Schaal et al.39 reported the case of a 27-year-old patient who presented with visible haematuria and a large abdominal mass. Abdominal CT revealed a large retroperitoneal mass, which was radiologically consistent with malignant neoplasm. Aspiration puncture of the lesion was carried out with a fine needle and a diagnosis of small cell malignant neoplasia was made. During staging, no distant lesions were seen and, in view of the large tumour volume, adjuvant chemotherapy was given. A chemotherapy protocol for Wilms’ tumour was reported, with 50 µg/kg acrinomycin and 0.04 mg/kg vincristine, for four cycles, obtaining minimal response and the tumour mass remained unresectable. Open biopsy of the lesion was carried out and histopathological examination of the biopsy specimen revealed a malignant neoplasm that was composed of two distinct cell populations, one consisting of small cells with round hyperchromatic nuclei and high mitotic index (poorly differentiated subtype with high malignancy grade) and the other of spindle cells with oval nuclei, fine chromatin, indistinct nucleoli and low mitotic index (monophasic fibrous subtype with low malignancy grade) surrounding renal tubules that were cystically dilated. The immunohistochemical study was reported to be consistent with synovial sarcoma: positive for pan-CK, EMA, vimentin and Bcl-2, and negative for CD99/MIC2, muscle-specific desmin and actin HHF-35. A 4-week chemotherapy cycle of 50 mg/kg ifosfamide and 1 mg/kg adriamycin was quickly initiated. As a result of considerable reduction of the tumour size (approximately 50%) a radical nephrectomy via right thoracoabdominal incision was undertaken with partial excision of the diaphragm and ascending colon. No macroscopically involved lymph nodes were found intraoperatively and microscopic examination of the specimen revealed an encapsulated tumour measuring 21 cm × 15 cm × 9 cm and weighing 1628 g with extensive areas of necrosis and haemorrhage. The adrenal gland, ureter and renal vein were not involved and the lymph node analysis was negative. The patient was followed up for 1 year with no evidence of recurrence.

Romero-Rojas et al.62 reported the case of a 15-year-old male who presented with a left-sided abdominal mass and weight loss. CT showed a 13 cm mass located in the lower pole of the left kidney. Histological examination of renal biopsy showed an undifferentiated neoplasm and immunohistochemistry suggested that the tumour was probably either a neuroectodermal primitive tumour or synovial sarcoma. Following chemotherapy and radical nephrectomy, macroscopic examination of the tumour showed a large multilobed necrotic tumour measuring 22 cm × 13 cm × 12.5 cm. Microscopic examination revealed that the neoplasm was composed of immature cells and the results of immunohistochemical studies gave a diagnosis of the PDSS small cell variety of the kidney. The patient, at the time of the case report, had survived for 1.8 years.

Moch et al.63 reported two cases of primary renal synovial sarcoma in the German literature but we do not have details of this report in the English literature. However, they stated that, on gross examination, the tumours were large, partially necrotic and contained cysts, and microscopic examination of the tumours revealed that the tumours were characterized by monomorphic plump spindle cells. The cysts were lined by mitotically inactive epithelial cells without any striking cellular atypia and the spindle cells were immunoreactive for EMA, CD56 and sometimes (focally) for CD99. They were non-reactive for desmin, actin, S100 and CK. The cyst epithelium was CK positive and the presence of a SYTSSX gene fusion resulting from the t(X,18) characteristic for synovial sarcoma was demonstrated by RT-PCR in both tumours. Moch et al.63 concluded that primary renal synovial sarcoma is a distinct tumour entity that should be considered in renal tumours consisting of spindle cells.

Divetia et al.38 described the clinicopathological, immunohistochemical and molecular analysis of seven cases of synovial sarcoma of the kidney, five females and two males (age range of 15–46 years), who presented with solitary renal masses ranging in size from 10.0 cm to 17 cm. Radical nephrectomy was performed in all cases and macroscopic examination revealed large, partially necrotic tumours containing smooth-walled cysts in four cases. Microscopic examination revealed that the tumours were characterized by monomorphic spindle cells with indistinct cell borders arranged in intersecting nodular foci with hypocellular myxoid areas, together with a prominent haemangiopericytomatous pattern. The cysts were lined by hobnailed cells with eosinophilic cytoplasm. Immunohistochemically, Bcl-2 was positive in all six cases, followed by vimentin (four out of five cases), MIC2 (two out of five cases), calponin (two out of two cases) and EMA (one out of four cases). Stains for CK and CD34 were consistently negative. RT-PCR using RNA extracted from formalin-fixed paraffin-embedded tissues was carried out in four cases and the SYTSSX fusion gene transcript, which is the diagnostic hallmark of synovial sarcoma, was detected. Two patients developed pulmonary metastasis and died at 6 and 12 months after diagnosis. The authors stated that this series of cases was distinct in terms of their morphological spectrum and confirmation of disease by molecular technique.

A number of other sporadic cases of synovial sarcoma of the kidney occurring in various age groups have been published including patients > 20 years37,61,62,6470 and teenagers.62,66,68

Conclusions

Approximately 64 cases of synovial sarcoma of kidney have been reported in the literature. Diagnosis of synovial sarcoma of the kidney is based upon characteristic microscopic findings that must be supported by specific diagnostic immunohistochemistry characteristics and molecular genetics evidence of chromosomal translocation t(X;18)(p11.2;q11,2).

Surgical excision including some surrounding normal tissue is the main treatment but there is evidence that ifosfamide- and doxorubicin-based chemotherapy may be beneficial for some patients.

Because of the rarity of synovial sarcomas of the kidney, urologists and oncologists need to report all cases of they encounter, together with reports of long periods of follow-up, to enable practitioners to fully understand the biological behaviour of such tumours.

Acknowledgement

Acknowledgement goes to The Korean Journal of Internal Medicine for granting permission to use images from their journal to illustrate the radiological, macroscopic and pathological appearances of synovial sarcoma of the kidney.

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