Immunohistochemical distinction of classic and chondroid chordomas.

Chondroid chordomas are cartilage-rich neoplasms, most often located in the spheno-occipital region, that have a better prognosis than classic chordomas. The immunohistochemical features of 19 classic and chondroid chordomas were studied retrospectively using avidin-biotin-complex (ABC) immunoperoxidase histochemistry on formalin-fixed, paraffin-embedded tissue. Of the 19 tumors, all located in the spheno-occipital region, 5 exhibited predominantly chondroid morphologic features. The 14 classic chordomas showed the following pattern of antigen expression (percent of tumors positive): epithelial membrane antigen (EMA) 100%, AE 1/3 (a "cocktail" of monoclonal antibodies directed against low and high molecular weight epidermal cytokeratins) 100%, DP keratin (DPK) 100%, vimentin 100%, S100 86%, neuron specific enolase (NSE) 100%, carcinoembryonic antigen (CEA) 57%, and HMB-45 (an anti-melanoma-associated antibody) 57%. The five chondroid chordomas exhibited the following pattern: EMA 0%, AE 1/3 0%, DPK 0%, vimentin 100%, S100 100%, NSE 100%, CEA 0%, and HMB-45 0%. The focal, weak HMB-45 positivity (performed on the index case because of a clinical concern of metastatic melanoma) seen in 57% of the classic chordomas is a previously unreported finding. This finding suggests either that classic chordomas are capable of HMB-45 expression or that this antibody has broader reactivity than previously recognized. The lack of cytokeratin, EMA, and CEA expression by the chondroid chordomas is similar to chondrosarcomas as reported in the literature and dissimilar to the classic chordoma group. These immunohistochemical findings suggest that chondroid chordomas may more validly be classified as low grade chondrosarcomas.