Clinicopathological features of usual ductal hyperplasia in the male breast. A case report

Background: Usual ductal hyperplasia (UDH) is a benign proliferative epithelial lesion frequently observed in female breast tissue but rarely reported in males. Due to its scarcity, the clinicopathological features and biological behavior of UDH in the male breast remain poorly defined. Case Presentation: A 19-year-old male presented with progressive left retroareolar breast enlargement of two years’ duration. Imaging revealed a well-circumscribed solid mass measuring 45 × 32 mm. A subcutaneous mastectomy was performed. Histopathological examination showed epithelial proliferation with micropapillary and cribriform architecture, preserved myoepithelial cells (p63 and smooth muscle actin positive), mosaic CK5/6 expression, diffuse estrogen receptor positivity, and a low Ki-67 index (