Case report: Metastasis of Merkel cell carcinoma in the small intestine.

Merkel cell carcinoma is a rare primary neuroendocrine malignant neoplasm of the skin, which recurs in about 40 % of cases. The main factors are Merkel cell polyomavirus (MCPyV) and mutations caused by ultraviolet radiation [Paulson, 2018]. In this study, we report a case of Merkel cell carcinoma with metastasis to the small intestine. In a 52-year-old woman, a subcutaneous formation of a nodule up to 2.0 cm in diameter was detected during the examination. This neoplasm was removed and sent for histological analysis. Dot-like expression of CK pan, CK 20, chromogranin A, and Synaptophysin was observed in tumor cells, and Ki-67 in 40 % of tumor cells. There is no reaction in tumor cells to CD 45, CK 7, TTF 1, and S100. The morphological picture corresponded to Merkel cell carcinoma. A year later, the patient underwent surgery for intestinal obstruction. The pathohistological changes and immunophenotype of the small bowel tumor were consistent with Merkel cell carcinoma metastasis.