A Case of Merkel Cell Carcinoma Arising on the Buttock

An 81-year-old female noticed a subcutaneous nodule on her left buttock almost 1 year before her first visit to us. Because of its rapid growth, the lesion was resected. On histological examination, a proliferation of small round tumor cells was observed in the deep dermis and the subcutaneous tissue. Nuclear atypia and mitotic figures were also detected in the tumor cells. The tumor cells were positive for cytokeratin 20 and chromogranin A. An analysis by PET-CT scanning showed no other systemic involvement, indicating the diagnosis of primary Merkel cell carcinoma arising on the buttock. We performed an additional wide resection. However, a left inguinal lymphadenopathy was noticed 6 months later, which was histologically diagnosed as a lymph node metastasis of Merkel cell carcinoma. A subsequent left inguinal lymph node dissection revealed no residual Merkel cell carcinoma and the patient has been free from recurrence for 6 months after the final operation. Merkel cell carcinoma preferentially develops on sun-exposed areas and its occurrence on the buttock is rare.