What Should You Do when DIN Is Found on Core Needle Biopsy?

Background: Flat ductal intraepithelial neoplasia (DIN) is a pathologic entity that is also known as flat epithelial atypia and is described to be a form of columnar cell hyperplasia of uncertain clinical significance. As widespread screening mammography has been implemented and more lesions are targeted for biopsy, the prevalence of this pathologic finding has increased, and there has been no clear consensus on follow-up. Objective: To determine whether surgical excision is warranted when DIN is found on core needle biopsy or vacuum-assisted biopsy of the breast. Methods: Biopsies that had been performed at 2 institutions over a 4-year period were reviewed. Cases where DIN was found on core needle biopsy or vacuum-assisted biopsy were identified. Lesions were only included in the study if no additional lesion, such as carcinoma or papilloma, was associated with the DIN. If the patients subsequently underwent surgical excision, the final pathology on surgical excision was reviewed to more...