CEA REACTIVITY IN AMELANOTIC MALIGNANT-MELANOMA OF THE ANAL-CANAL

Amelanotic malignant melanoma can present a diagnostic problem in hist opathology, especially when it presents in an extracutaneous location. In such cases electron microscopy and/or immunohistochemistry are inv aluable for diagnosis. A 63-year-old woman with rectal bleeding was fo und to have an amelanotic malignant melanoma of the anal canal, with c ompatible clinical and gross pathology and light and electron microsco pic findings. Tumor cells showed positive staining with antibodies to vimentin, S 100 protein, and HMB-45 (melanoma-specific antibody), but also with polyclonal antibody to carcinoembryonic antigen (CEA). Tumor cells failed to stain with monoclonal antibody to CEA. The nature and significance of CEA reactivity in malignant melanoma are discussed.