Collagenous spherulosis presenting as a mass of the breast

Collagenous spherulosis (CS) is a rare benign lesion which typically presents as an incidental microscopic finding accompanying other breast lesions. Pathologists who are not familiar with this entity occasionally misdiagnose CS as adenoid cystic carcinoma (ACC), cribriform ductal carcinoma in situ (C-DCIS), or atypical intraductal hyperplasia (AIH), especially when it presents as a mass. It is of utmost importance to differentiate benign CS from its malignant mimics in order to avoid unnecessary treatment. We report an unusual case of CS manifested as a mass in the right breast of a 45-year-old female and discuss the problems of differential diagnosis and histogenesis.