Pathology of B3 lesions of the breast

Breast needle core biopsy is a widely used technique for evaluation of mammographic and clinical breast abnormalities, screen detected and symptomatic. The majority of biopsies can be coded as B2 (benign) or B5 (malignant). However, certain lesions merit a B3 designation, signifying ‘uncertain malignant potential’. This is a heterogenous group including atypical intraduct epithelial proliferation, lobular neoplasia, radial scar, papillary lesions and columnar cell change. Their common denominator is the low but significant rate of malignancy within the lesion or adjacent tissue, necessitating excision biopsy for full histological examination. In this article we review the morphology and biological significance of B3 entities.