In order to determine epithelial markers in malignant melanoma in routinely processed paraffin sections and to compare the staining of primary (cutaneous) malignant melanomas and their metastases, we stained formalin-fixed paraffin sections of 13 primary and 18 metastatic malignant melanomas using the streptavidin-biotin peroxidase method by antibodies to S-100, vimentin, HMB-45, polyclonal carcinoembryonic antigen (CEA), monoclonal CEA, cytokeratins (CAM 5.2 and broad-spectrum CKKES), and epithelial membrane antigen (EMA). All primary and most metastatic malignant melanomas showed positive staining with anti-S-100, HMB-45, and anti-vimentin. Reactivity with polyclonal CEA was observed in 15 (48%) of the 31 lesions; 14 of them were metastatic. No lesion was reactive with monoclonal CEA. Significant cytokeratin (CK) staining was evident in only three (9.7%) lesions (all metastatic), which also stained specifically with anti-CK 18. EMA was observed only focally in two (6.5%) lesions. There was no correlation between epithelial markers staining of the primary tumours and their metastases. All lesions with CK or EMA staining showed concomitant extensive staining for S-100, HMB-45, and vimentin. We conclude that (a) polyclonal CEA staining in malignant melanoma is not rare and is probably due to CEA-related molecules; (b) significant CK reactivity is rare and related to simple CK, such as CK 18; (c) epithelial marker reactivity is more common in metastases of malignant melanomas and is not correlated to the reactivity in their primary tumors. Considering our results and reports of positive S-100, vimentin, and HMB-45 in epithelial tumors, a wide panel of antibodies is recommended for the study of undifferentiated tumors.
