Merkel cell carcinoma with spontaneous regression

Merkel cell carcinoma (MCC) is a malignant neuroendocrine tumor and has a high rate of recurrence and metastasis. On the other hand, some cases of spontaneous regression have recently been reported. We describe here the clinical course of an 80-year-old Japanese woman with regressing MCC. After the patient's first visit to our hospital, the lesion was a rapidly progressing tumor. However, the tumor was noted to suddenly begin decreasing in size, and rapidly regressed. The surface of tumor became flattened and the color of the tumor changed from red to dark red, and finally the lesion appeared as a small yellowish plaque. We also analyzed the completely regressed tumor histopathologically. The results revealed that the tumor cells were completely replaced by numerous foamy cells.