Apocrine Hidrocystoma of the Breast Mimicking an Epidermal Inclusion Cyst

Apocrine hidrocystomas are rare, benign cystic tumors arising from apocrine sweat glands, with a predilection for the head and neck, most commonly involving the eyelids. Occurrence within breast tissue is exceptionally uncommon and represents a diagnostic challenge, particularly given the high prevalence of other cystic lesions in this location. We report a 67-year-old female who presented for excision of a new, painless right breast nodule detected on self-examination. She had a known history of dense breast tissue and benign breast masses. Ultrasonography identified a hypoechoic lesion consistent with an epidermal inclusion cyst. Clinical examination revealed a firm, flesh-colored nodule with a small light-brown macule on the overlying skin, further supporting this diagnosis. During excision, clear watery fluid was expressed, an atypical intraoperative finding inconsistent with the expected thick keratinaceous contents of an epidermal inclusion cyst. Histopathologic analysis demonstrated a multiloculated cyst lined by apocrine epithelium with characteristic features, confirming the diagnosis of apocrine hidrocystoma. This case contributes to the limited literature on breast apocrine hidrocystoma and underscores the value of clinicopathologic correlation when evaluating cystic lesions in atypical anatomic locations.