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 for which clinical follow-up information was available.
Tumors were restaged using NWTS 5 criteria. Mean age at diagnosis in the NWTS group was 36 months 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 mucoid texture, foci of
necrosis, and prominent
cyst formation. Nine major histologic patterns were identified (classic, myxoid, sclerosing, cellular, epithelioid, palisading, spindle, storiform, and anaplastic); virtually all
tumors contained multiple patterns that blended with one another. Immunohistochemical stains were performed on 45 cases; only
vimentin was consistently immunoreactive. Consistently negative results with other
antibodies helped exclude other
tumors in the differential diagnosis; all CCSKs were
cytokeratin-negative, including epithelioid
tumors that mimicked
Wilms tumor, and MIC2-negative, including cellular
tumors that mimicked
primitive neuroectodermal tumor. The p53 gene product was rarely overexpressed in non-anaplastic CCSKs, but strikingly overexpressed in two of three anaplastic CCSKs. Overall survival was 69%. Multivariate analysis revealed four independent prognostic factors for survival: treatment with
doxorubicin, stage, age at diagnosis, and
tumor necrosis. Of note, stage 1 patients had a remarkable 98% survival rate. No other histologic or clinical variable independently correlated with survival.