Primary signet-ring cell carcinoma of the axilla.

Primary cutaneous histiocytoid or signet-ring cell carcinoma represents an extremely rare adnexal neoplasm that most frequently presents on the eyelid but more rarely may present in the axilla. As this tumor can resemble metastatic carcinoma with signet-ring cells, especially lobular carcinoma of the breast, it can often present a diagnostic challenge. We present a case of cutaneous signet-ring cell carcinoma presenting in the axilla and outline the challenges of diagnosing this rare malignancy.