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 (mean 63.11 +/- 16.24; median 62.5) was performed. 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 can be interpreted as metastases from MCC, if they demonstrate the phenotype Cytokeratin, Ran AE1 /AE3 (paranuclear +) /CK20 (paranuclear +) / Vimentin (-) /CD45 (-) / S100 (-) / Chromogranin A (+) / Synaptophysin (+), as well as possess nuclei, the area and perimeter of which are 2 times higher than that of normal lymphocytes (all p> 0.05). Conclusions. Metastatic MCC without primary localization, in comparison with locally spreading, often demonstrate low- differentiated small- cell and transitional forms, which require additional immunohistochemical studies to exclude metastases of carcinoma of other origin.