SARCOMATOID RENAL-CELL CARCINOMA - AN IMMUNOHISTOCHEMICAL STUDY OF 18CASES

Malignant spindle cell neoplasms are a diagnostic challenge regardless of their location. In the retroperitoneum a major consideration in th e differential diagnosis is sarcomatoid renal cell carcinoma; if an ep ithelial component cannot be recognized histologically, special studie s may be required to reach the correct diagnosis. In an attempt to bet ter characterize this entity, 23 cases of sarcomatoid renal cell carci noma (6.3%) were identified from a review of 363 renal cell carcinomas . Blocks were available for immunohistochemical analysis in 18 cases. The epithelial and sarcomatoid portions were studied with a panel of a ntibodies directed against cytokeratin (AE1/AE3, CAM 5.2, and 34betaE1 2), epithelial membrane antigen, Leu-M1, muscle-specific actin, Sl 00 protein, desmin, and vimentin. The epithelial nature of the spindle ce ll component was best demonstrated by positive reactivity with the ant i-cytokeratin AE1/AE3 (in 17 [94%] of the 18 cases). The other epithel ial markers stained the spindle cell component less frequently: cytoke ratin CAM 5.2 in seven cases (39%); epithelial membrane antigen in nin e cases (50%); and high-molecular-weight cytokeratin 34betaE12 in no c ases (0%). In 10 cases (56%) vimentin positivity and in six cases (33% ) actin positivity was seen in the spindled areas. The spindle cell co mponent stained for Leu-Ml in four cases (22%) and for Sl 00 protein i n one case (6%) and did not react for desmin in any case. From this st udy we conclude that in the majority of sarcomatoid renal cell carcino mas the epithelial nature of the spindle cells, as indicated by cytoke ratin expression, can be documented using immunohistochemical methods.