Mucinous adenocarcinoma in the axilla of undetermined origin.

Mucinous adenocarcinoma (MAC), accounts for ⁓1% of all cancer diagnoses. We present a case of a 75-year-old male who, after presenting for an elective inguinal hernia repair, disclosed concerns for a new lesion in his right axilla which was removed at the same time. Investigations revealed a MAC of unclear origin, with immunohistochemistry suggesting either a breast or primary cutaneous mucinous adenocarcinoma (PCMC). The patient was asymptomatic with an otherwise normal examination. Extensive investigations failed to identify any primary source. Axillary node clearance was performed, resulting in 0/9 positive nodes. After multi-disciplinary team discussion, this patient (who remains asymptomatic) will be kept under close clinical surveillance, with yearly computerized tomography scans. To our knowledge, minimal presentations have been reported in the literature. Thus, our case report is a unique addition of an atypical presentation of PCMC in the axilla.