AN IMMUNOHISTOCHEMICAL COMPARISON OF CHORDOMA WITH RENAL-CELL CARCINOMA, COLORECTAL ADENOCARCINOMA, AND MYXOPAPILLARY EPENDYMOMA - A POTENTIAL DIAGNOSTIC DILEMMA IN THE DIMINUTIVE BIOPSY

Chordoma is one of several similar appearing neoplasms in the retroper itoneum, pelvis, and abdomen with a combination of features including clear cells, with or without cytoplasmic vacuoles, papillary profiles, and a myxoid or myxohyaline stroma. The differential diagnosis of a c ellular myxoid or mucinous tumor in a small biopsy, when the entire tu mor is not available for pathologic examination, includes metastatic m ucinous adenocarcinoma of colorectal and other similar-appearing neopl asms, renal cell carcinoma, and myxopapillary ependymoma. We compared immunohistochemical reactivity of 18 chordomas with 20 colonic adenoca rcinomas, 20 renal cell carcinomas, and six myxopapillary ependymomas using antibodies to vimentin, cytokeratin, epithelial membrane antigen , S100 protein, Leu 7, glial fibrillary acidic protein, and carcinoemb ryonic antigen. All chordomas were immunreactive for vimentin and cyto keratin, 83% for epithelial membrane antigen, and 83% for S100 protein . Myxopapillary ependymomas were distinguished by immunoreactivity for vimentin and glial fibrillary acidic protein in all cases and S100 pr otein in 50%. All colonic adenocarcinomas were positive for cytokerati n, epithelial membrane antigen, and carcinoembryonic antigen. Renal ce ll carcinomas were uniformly reactive for epithelial membrane antigen and cytokeratin, nonreactive for carcinoembryonic antigen, and variabl y reactive for S100 protein (5%) and vimentin (25%). These data indica te that a panel of immunohistochemical markers can be useful in distin guishing chordoma from potential histologic mimics.