Comparative analysis of clinicopathological and immunohistochemical characteristics of Merkel cell carcinoma

To investigate both the clinicopathological and immunohistochemical characteristics of a very rare skin cancer - Merkel cell carcinoma (MCC) - and to review the relevant literature. The study group was composed of 12 patients, with mean age 53.08±10.26 years. Multiple subcutaneous masses and lymph node metastases were surgically removed. Paraffin blocks of formaldehyde-fixed tumor tissue were cut and stained for histological, histochemical and immunohistochemical studies. The following antibodies (Dacopatt) were used: Chromogranin A, CK20, CK7, Melan A, CD20 and CD45Ro. The tumors involved the dermis while sparing the epidermis. The most frequently affected sites were sun-exposed skin (8 patients on the head and neck) and the most common histological subtype of MCC was the intermediate variant. Six patients had lymph node metastasis and 2 had locoregional recurrences. Haematogenous lung metastases of MCC and primary located in the trunk were found only in our youngest patient (36-year-old). Immunostaining revealed positive reactivity for neuroendocrine and epithelial markers and negative reactivity for melanoma, B/T lymphomas and small cell metastatic lung carcinoma. MCC is a rare malignant primary cutaneous neoplasm with epithelial and neuroendocrine differentiation, demanding wide local excision. The pathological differential diagnosis includes basal cell carcinoma, melanoma, lymphoma, and metastatic small cell lung carcinoma. The diagnosis of MCC is possible only immunohistochemically, by using the wide spectrum of antibodies, characteristic of microscopically similar tumors.