We report a case of intraepidermal
Merkel cell carcinoma which occurred on the face of a 76-year-old white male. This slow-growing
tumor was mostly confined in the epidermis and pilosebaceous apparatus where
tumor cells spread in a pagetoid fashion forming
tumor cell nests. Histologically it resembled a superficial spreading
melanoma. A heavy lymphocytic infiltration was seen beneath the epidermal lesion as is often seen in pagetoid
melanomas. Histochemical and ultrastructural features such as the presence of
cytokeratin 20,
synaptophysin,
neuron specific enolase, desmosomes, and dense cored granules confirmed the diagnosis of
Merkel cell carcinoma. Occasional mitotic cells and many apoptotic cells were found in the
tumor.
Dylon positive,
amyloid depositions were seen in the lower epidermis and papillary dermis; they were probably derived from apoptotic
tumor cells. It was thought that apoptosis limited the speed of growth of this
tumor. We believe that this is probably the most convincing case of intraepidermal
Merkel cell carcinoma originating from epidermal Merkel cells or its precursors (stem cells).