Epithelial markers in malignant melanoma. A study of primary lesions and their metastases

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.