MAML2 ‐Rearranged Hidradenoma of the Breast: Clinicopathologic and Molecular Analysis of Four Patients

Hidradenoma (HA) is a rare, benign adnexal tumor typically arising in the skin, with only a few reported cases in the breast. Histologically, HA displays solid and cystic patterns with diverse cellular components. Although MAML2 gene rearrangement is observed in some cutaneous HAs, its significance in breast HA remains unclear. We retrospectively analyzed four cases of breast HA at our institution, focusing on clinicopathologic and molecular characteristics. MAML2 rearrangement was detected in all cases by FISH, suggesting it may be a defining feature of breast HA. Because breast HA frequently mimics malignancy and is often diagnosed only after excision, heightened awareness and recognition of its distinctive clinicopathologic and molecular features are essential to prevent overtreatment.