Spontaneous regression of merkel cell carcinoma

Abstract

Merkel cell carcinoma is a malignant neuroendocrine tumor with a high rate of recurrence and metastasis. However, approximately 23 cases of spontaneous regression have been reported. We report a case of Merkel cell carcinoma which showed spontaneous regression. The patient was an 84-year-old male with a large red-colored, hemispheric tumor on the left inner thigh which had been presented for a year. We planned to perform surgery, but the tumor suddenly started to regress spontaneously. The size of the tumor decreased, the surface was flattened, and the color changed from red to brown. The lesion finally appeared as a brownish flat plaque. Excision of the regressed tumor was performed; immunohistopathological analysis showed CD3+ T cells infiltrating around the regressed merkel cell carcinoma.