Clinical and pathological features of primary renal synovial sarcoma: analysis of 64 cases from 11 years of medical literature

Study Type – Prognosis (case series) Level of Evidence 4 What's known on the subject? and What does the study add? Primary renal synovial sarcoma is a very rare renal neoplasm. Since 2000, when this tumour was first described, only case reports have been published in the medical literature. This study is the first to describe the clinical and pathological features of primary renal synovial sarcoma and it found a relationship between these characteristics. Median overall and disease‐free survival were reported, and the risk of relapse for patients with non‐metastatic disease at diagnosis was found to be 36%. Different histological sub‐types, also described in other synovial sarcomas, were found in primitive renal tumours and directly related to tumour extension at diagnosis, different patterns of immunohistochemical stain and genetic alterations. OBJECTIVE To describe, for the first time, the clinical characteristics of primary renal synovial sarcoma (SS) and to examine the association of histological features with the expression of immunohistochemical markers. PATIENTS AND METHODS We collated published data on all cases of primary renal SS, from its first description in 2000 to September 2011. Data on clinical and pathological characteristics were extracted and used to create a database. Disease‐free survival (DFS) and overall survival (OS) rates were estimated using the Kaplan–Meier method with Rothman's 95% confidence intervals (CIs) and compared across the groups using the log‐rank test. The associations between tumour extension and histological features were evaluated using the non‐parametric Spearman rank test. A chi‐squared test was used to assess the differences between groups. RESULTS In the overall cohort, the median OS was 48 months (95% CI, 14.1–81.9). Cox analysis showed that the risk of death at diagnosis was greatly increased in patients with metastatic disease compared with those with non‐metastatic disease (hazard ratio [HR]: 343.9, 95% CI, 2.8–42 000; P = 0.017). The median DFS was 33.0 months (95% CI, 16.8–49.2), and patients who develop metastatic disease have a very poor prognosis with a median survival of 6 months (95% CI, 5.1–6.9). Microscopic features were monophasic, biphasic and poorly differentiated synovial sarcoma in 76, 16 and 8% of patients, respectively. Significant differences in expression of immunohistochemical markers or genetic mutation were found between different subtypes. CONCLUSIONS Despite its retrospective nature, this study shows that renal SS comprises different histological subtypes, which are characterized by specific immunohistochemical stains and by specific translocations. When diagnosed at metastatic stage, the prognosis was very poor compared with that for non‐metastatic disease, even though one out of three patients with non‐metastatic disease had disease relapse. Cooperative efforts and publication of cases with adequate follow‐up are necessary to better define prognosis and therapeutic strategies for this rare disease.