Primary cutaneous mucinous carcinoma initially diagnosed as metastatic adenocarcinoma

The authors report a rare case of primary mucinous carcinoma of the skin initially diagnosed as a metastatic adenocarcinoma. The tumor occurred in the right axilla in a 75-year-old man. Initial pathological diagnosis was metastatic adenocarcinoma. However, no primary focus was found in the body. The revised diagnosis by the authors was primary cutaneous mucinous carcinoma. The tumor (1.5 cm) was characterized by proliferation of atypical epithelial cells arranged in cell nests with many pseudolumens resembling adenoid cystic carcinoma. It was also characterized by much mucinous stroma or pool around tumor cells. No apparent eccrine or apocrine differentiation was noted histologically and immunohistochemically. The present case suggests that primary cutaneous mucinous carcinoma may be misdiagnosed as metastatic adenocarcinoma, and that it may resemble adenoid cystic carcinoma.