Primary undifferentiated small cell carcinoma (Merkel cell carcinoma) in a patient after heart transplantation--case report.

Here we report a case of a 48-year-old man after heart transplantation in whom two years after the procedure an appendage germ tumour was diagnosed and a year after its removal in the same area a primary undifferentiated small cell carcinoma (Merkel cell carcinoma) with metastases to the axillary lymph nodes was detected. The diagnosis of Merkel cell carcinoma was confirmed by immunohistochemical staining showing a typical perinuclear expression of cytokeratin 20 with the absence of reactivity with wide spectrum cytokeratin and the presence of neuroendocrine markers of neurone-specific enolase and chromogranin. Primary undifferentiated small cell carcinoma occurs more frequently in patients receiving immunosuppressive treatment as compared with a general population and occurs much more frequently in those below 50 years of age.