Predictive value of needle core biopsy diagnoses of lesions of uncertain malignant potential (B3) in abnormalities detected by mammographic screening

Breast needle core biopsy (NCB) is now a commonplace diagnostic procedure in breast cancer screening, providing accurate diagnoses of both benign and malignant lesions. However, NCB may result in the borderline diagnoses of lesion of uncertain malignant potential (B3) or suspicious of malignancy (B4). The aim was to study a large series of B3 cases from population-based screening subjects in order to evaluate positive predictive values (PPVs) for malignancy. The results of 523 NCBs of women screened over a 7-year period (1999-2006) in the East Midlands region, UK, with a B3 diagnosis who underwent surgical excision, were reviewed and compared with the final excision histology. Five percent of NCBs were reported as B3. The most frequent histological subtypes were atypical intraductal epithelial proliferation (AIDEP) and radial scar/complex sclerosing lesion (RS/CSL). Final excision histology was benign in 417 (80%) and malignant in 106 (20%) subjects (60 ductal carcinoma in situ and 46 invasive carcinoma). Lesion-specific PPVs were as follows: AIDEP 32%; lobular neoplasia (LN) 30%; RS/CSL with AIDEP or LN 24%; RS/CSL without atypia 9%; papillary lesion with AIDEP or LN 36%; and papillary lesion without atypia 4%. Five of the 32 fibroepithelial lesions with cellular stroma were phyllodes tumours (four benign and one borderline). None of the five mucinous lesions on NCB was malignant. Our results show that approximately one-fifth of NCB of screen-detected breast lesions classified as B3 are malignant on excision, and the likelihood of malignancy varies substantially between different histological subtypes.