Screen-detected breast lesions with an indeterminate (B3) core needle biopsy should be excised

Background: Screen-detected breast lesions in the National Health Service Breast Screening Programme (NHSBSP) are assessed by core needle biopsy (CB) or fine needle aspiration cytology (FNAC). Most core biopsies are diagnostic and representative, but a small proportion is indeterminate (coded "B3" in the NHSBSP). We studied the surgical outcome of screen-detected breast lesions with indeterminate (B3) CB. Methods: We retrieved and analysed the data on women who were recalled for assessment of a screen-detected abnormality in whom the initial CB was reported as B3 over a six-year period from a prospectively collected database in one breast screening centre. The main outcome measure was final histology following surgical excision. Results: Among 4080 CB performed, 220 (5.4%) were B3. Mammographically 127 lesions were microcalcifications and 88 were soft tissue lesions. On surgical excision (n = 199, 90%), 67 (34%) were malignant. In patients with malignancy, clinical examination, US and concurrent FNAC were either suspicious or definitive of malignancy only in 2%, 4% and 7%, respectively. Conclusion: A third of screen-detected breast lesions with indeterminate CB are malignant on excision. Clinical examination, US, and FNAC may identify some of these carcinomas pre-operatively but most malignancies would not be picked up. Thus, these lesions should undergo surgical excision.