Primary mucinous carcinoma of the skin with metastases to the lymph nodes.

Primary mucinous carcinoma is a rare sweat-gland neoplasm of the skin with a tendency to grow slowly. Although the neoplasm persists locally in nearly half of the cases after attempts at removal, metastases to regional lymph nodes and widespread metastases are uncommon. We present a case of primary mucinous carcinoma in an axilla with metastases to the axillary lymph nodes and propose a hypothesis explaining the slow rate of growth, based on our findings of a paucity of both blood vessels and macrophages in the neoplasm. Electron microscopy revealed mucin production by the dark cell and its extracellular secretion, which supports the theory of eccrine differentiation of the neoplasm.