Characterization and outcome of breast needle core biopsy diagnoses of lesions of uncertain malignant potential (B3) in abnormalities detected by mammographic screening.

In the setting of breast cancer screening, 5-9% of needle core biopsies are diagnosed as lesions of uncertain malignant potential (B3). The management of these lesions is potentially problematic as the data on their outcome remains limited. In our study, we aim to assess the outcome of screen-detected lesions diagnosed as B3 in a large series to validate previous studies and to characterize the malignant lesions detected after a B3 diagnosis. Therefore, the results of 1,025 needle core biopsies of women screened over a 7-year period (1999-2006) in two different regions in the UK with B3 diagnoses who underwent surgical excision were reviewed and compared to the final excision histology. Final histology showed that 25% of cases were malignant (17% ductal carcinoma in situ and 8% invasive). Predictors of malignancy included calcification on imaging and epithelial atypia on needle core biopsy particularly atypical ductal hyperplasia [positive predictive value 50%]. Pure flat epithelial atypia showed the lowest positive predictive value amongst all epithelial atypia groups (21%). The positive predictive value was low for complex sclerosing lesions (9%) and papillary lesions (13%) without epithelial atypia. Malignant tumors detected after B3 diagnosis showed favorable histological features, the majority were in situ, and most belonged to the low grade breast neoplasia family that is associated with indolent behavior. The underlying radiological abnormality was calcification in 44% of cases and the imaging classification was malignant/suspicious in 38%. In conclusion, our results further emphasize the heterogeneity of B3 lesions and that the likelihood of malignancy varies substantially between different histological subtypes. Malignancy is particularly associated with epithelial atypia suggesting the use of two categories of with and without epithelial atypia. Radiological findings provided useful information regarding the nature and outcome of B3 lesions.