Metastases of Merkel cell carcinoma in terms of diagnosing carcinomas with unknown primary localization

Merkel cell carcinoma (MCC) is a rare malignant primary skin neoplasia with epithelial and neuroectodermal differentiation. The problem of MCC, which determines the relevance of its research, is often a high frequency of local recurrence, regional lymph node metastasis and further hematogenous and/or distant lymphogenous dissemination. Materials and methods. A retrospective analysis of the biopsy material of 6 patients with isolated MCC metastasis aged from 29 to 82 years (average 63.11 ± 16.24; median 62.5) was carried out. For the control group, 9 cases of postoperative material of primary skin tumors with MCC of patients aged from 27 to 76 years (average 52.17 ± 12.72; median 53.5) were selected to determine the differential diagnostic criteria. The results of the study. Carcinomas without primary localization may be interpreted as MCC if they demonstrate phenotype Cytokeratin, Pan AE1/AE3 (paranuclearly +) / CK20 (paranuclearly +) / Vimentin (-) / CD45 (-) / S100 (-) / Chromogranin A (+) / Synaptophysin (+), with morphometric parameters of the area and perimeter, which is 2 times the size of ordinary lymphocytes, (all p>0.05). Findings. Metastatic CMC without primary localization, in comparison with locally spreading, often exhibit low-differentiated small-cell and transitional forms, which require additional immunohistochemical study to exclude carcinomas of other origin.