Primary Cutaneous Mucinous Carcinoma with Extramammary Paget's Disease: Eccrine or Apocrine?

Primary cutaneous mucinous carcinoma (PCMC) is an uncommon tumor of the sweat gland origin. The occurrence of PCMC is mostly in middle-aged and older patients, with a slight male predominance. Most cases of PCMC arise on the head, with a preference for eyelids. The histogenesis of PCMC, whether eccrine or apocrine, remains controversial. We report a rare case of PCMC with secondary extramammary Paget's disease in the groin of a 75-year-old man, which favored an apocrine origin. Furthermore, based on a review of the literature, we provide several histologic clues that can be used to differentiate PCMC from metastatic mucinous carcinoma.