Ns. House et al., MALIGNANT-MELANOMA WITH CLINICAL AND HISTOLOGIC FEATURES OF MERKEL CELL-CARCINOMA, Journal of the American Academy of Dermatology, 31(5), 1994, pp. 839-842
We describe a patient with malignant melanoma that resembled a Merkel
cell carcinoma both clinically and histologically. Immunohistochemical
studies showed focally positive staining with S-100 protein and stron
gly positive staining with HMB-45. Ultrastructural study confirmed the
diagnosis by demonstrating premelanosomes and melanosomes. Although t
he tumor appeared to be clinically unimpressive, it was a deep melanom
a with a Breslow level of 3.8 mm that necessitated aggressive treatmen
t. Small cell melanoma must be considered in the differential diagnosi
s of small cell tumors, which also includes lymphoma, eccrine carcinom
a, squamous cell carcinoma, and Merkel cell carcinoma. The diagnosis o
f amelanotic melanoma, including the small cell variant, may require e
lectron microscopic studies.