2024 Volume 39 Issue 2 Pages 169-173
A 72－year－old man observed a painless nodule on his left buttock 3 months before he visited a clinic. No significant changes occurred during this period. The nodule was surgically removed at the clinic ; however, histopathological findings indicated Merkel cell carcinoma, and he was referred to our department for further management. The patient presented with a pea－sized subcutaneous nodule on the left buttock, without any surface changes or palpable inguinal lymph nodes. The serum neuron－specific enolase level was normal at 8.7 ng/mL, and positron emission tomography－computed tomography showed no signs of metastasis. Histopathological evaluation showed a tumor in the dermis, with a pattern of irregular nest formation and fibrous stroma. The tumor cells were small and round, with scant cytoplasm, slightly varying nuclei, and rare mitotic figures. Immunohistochemistry revealed cells with CK20 immunopositivity in a dot－like pattern at the nuclear periphery together with immunopositivity for CAM5.2, synaptophysin, chromogranin A, and CD56. Sentinel lymph node biopsy of the left inguinal region did not reveal tumor cells. Postoperatively, the patient was administered radiotherapy (60 Gy) to the primary site and associated lymph nodes. No recurrence or metastasis was observed at the 4－year follow－up. Merkel cell carcinoma of the buttocks is rare. In this report, we summarize the characteristics of Merkel cell carcinoma of the buttocks.[Skin Cancer (Japan) 2024 ; 39 : 169－173]
