Clear cell sarcoma of the kidney - A review of 351 cases from the NationalWilms Tumor Study Group Pathology Center

We reviewed 351 cases of clear cell sarcoma of the kidney (CCSK), including 182 cases entered on National Wilms Tumor Study Group (NWTSG) trials 1-4 f or which clinical follow-up information was available. Tumors were restaged using NWTS 5 criteria. Mean age at diagnosis in the NWTS group was 36 mont hs with a range of 2 months to 14 years. The male to female ratio was 2:1. Typical gross features included large size (mean diameter 11.3 cm), a mucoi d texture, foci of necrosis, and prominent cyst formation. Nine major histo logic patterns were identified (classic, myxoid, sclerosing, cellular, epit helioid, palisading, spindle, storiform, and anaplastic); virtually all tum ors contained multiple patterns that blended with one another. Immunohistoc hemical stains were performed on 45 cases; only vimentin was consistently i mmunoreactive, Consistently negative results with other antibodies helped e xclude other tumors in the differential diagnosis; all CCSKs were cytokerat in-negative, including epithelioid tumors that mimicked Wilms tumor, and MI C2-negative, including cellular tumors that mimicked primitive neuroectoder mal tumor. The p53 gene product was rarely overexpressed in non-anaplastic CCSKs, but strikingly overexpressed in two of three anaplastic CCSKs. Overa ll survival was 69%. Multivariate analysis revealed four independent progno stic factors for survival: treatment with doxorubicin, stage, age at diagno sis, and tumor necrosis, Of note, stage 1 patients had a remarkable 98% sur vival rate. No other histologic or clinical variable independently correlat ed with survival.