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A review of the literature on synovial sarcoma of the kidney
Synovial cell sarcomas of the kidney are rare tumours that most urologists and pathologists throughout the world have not encountered. Because of this, most practitioners may not be aware of the presentation, diagnostic features or biological behaviour of such tumours. This article reviews the literature on synovial cell sarcomas of the kidney in order to document the presentation, investigation, management as well as outcome following treatment of these tumours. Synovial sarcoma of the kidney is a rare tumour that was first reported in 1999 and, since then, 64 cases have been reported in the literature. Synovial sarcomas of the kidney tend to be found in patients who are aged between 17 and 61 years, and the clinical presentation and radiography findings are similar to those of other renal tumours. There are three main types of primary synovial sarcomas of the kidney: the biphasic, the monophasic and the poorly differentiated varieties. Primary biphasic synovial sarcomas contain both glandular elements and spindle epithelial cells, whereas primary monophasic synovial sarcomas are composed of spindle cells only and poorly differentiated synovial sarcomas (PDSSs) exhibit three histological variants: large cell, small cell and high-grade spindle cell variant. PDSSs are composed of sheets of undifferentiated round cells with hyperchromatic nuclei and frequent mitoses, and such tumours are often associated with a rich vascular pattern with dilated and thin-walled vascular spaces that resemble haemangiopericytoma. The differential diagnoses include adult Wilms’ tumour, transitional cell carcinoma, renal cell carcinoma, haemangiopericytoma, congenital ectoblastic nephroma and primitive neuroectodermal tumour (PNET). Diagnosis of renal synovial sarcoma is based on microscopic findings of (a) spindle cells (monophasic) or (b) glandular cells and spindle cells (biphasic) supported by immunohistochemical staining characteristics [positivity for CD99, CD56, Bcl-2, epithelial membrane antigen (EMA) and cytokeratin (CK)] and molecular genetic studies of the tumour showing characteristic chromosomal translocation t(X;18)(p11.2;q11.2), which is seen in cases of synovial sarcoma. There is no consensus regarding the treatment of synovial sarcoma of the kidney; however, surgical excision including a portion of surrounding normal tissue (radical nephrectomy) has so far been the main treatment. In addition, response to ifosfamide and doxorubicin (adriamycin) chemotherapy has been reported. Recurrence following treatment for non-metastatic synovial sarcoma is approximately 36% and prognosis for advanced disease is poor. Diagnosis of synovial sarcoma of the kidney is based upon characteristic microscopic findings that must be supported by specific diagnostic immunohistochemistry characteristics and molecular genetic evidence of chromosomal translocation. Because of the rarity of synovial sarcomas of the kidney, urologists and oncologists need to report all cases they encounter, together with reports of long periods of follow-up, to enable practitioners to fully understand the biological behaviour of such tumours.