BACKGROUND - Clinical decisions about atypical lobular hyperplasia are based on the belief that later invasive breast-cancer risk is equal in both breasts. We aimed to show laterality and subsequent risk implications of invasive breast cancer in women with atypical lobular hyperplasia.
METHODS - We did a retrospective cohort study of 252 women who had undergone 261 benign surgical biopsies that showed atypical lobular hyperplasia from 1950 to 1985, as part of the Nashville Breast Studies. Primary outcomes were development of invasive breast cancer and laterality of cancer compared with side of the biopsied breast.
FINDINGS - 50 (20%) of 252 women treated by biopsy only developed invasive breast cancer. Relative risk of breast cancer in women with atypical lobular hyperplasia was 3.1 (95% CI 2.3-4.3, p<0.0001). Of these 50 women, the breast with invasive cancer was the same breast diagnosed with atypical lobular hyperplasia (ipsilateral) in 34 (68%) and the contralateral breast in 12 (24%). The ratio of ipsilateral/ contralateral cancers for atypical lobular hyperplasia without other atypical lesions was 17/5. For six women with atypical lobular hyperplasia plus atypical ductal hyperplasia, the ratio was 1/1.
INTERPRETATION - Invasive carcinoma after atypical lobular hyperplasia is about three times more likely to arise in the breast diagnosed with atypical lobular hyperplasia than in the opposite breast without these initial findings. Our findings suggest a model of premalignancy for atypical lobular hyperplasia intermediate between a local precursor and a generalised risk for both breasts. See Commentary page 96