Collagenous spherulosis of the breast is distinctive breast histological finding characterised by the accumulation of basement membrane material in form of eosinophilic or rarely basophilic spherules that exhibit concentric and radiating fibrillar patterns. It is usually an incidental microscopic uni- or multifocal finding that occurs adjacent to benign proliferative lesions, but it can be also coexistent with malignant breast processes. Its occurrence within a malignant process is exceptional. We present a case of collagenous spherulosis of the breast associated with poorly differentiated carcinoma in situ in a 54-year-old woman. This rare change can be misinterpreted as adenoid cystic carcinoma.