Women with
atypical ductal hyperplasia (ADH), atypical lobular
hyperplasia (ALH),
lobular carcinoma in situ (LCIS), and severe ADH are at increased risk of
breast cancer, but a systematic quantification of this risk and the efficacy of
chemoprevention in the clinical setting is still lacking. The objective of this study is to evaluate a woman's risk of
breast cancer based on atypia type and to determine the effect of
chemoprevention in decreasing this risk. Review of 76,333 breast pathology reports from three institutions within Partners Healthcare System, Boston, from 1987 to 2010 using natural language processing was carried out. This approach identified 2,938 women diagnosed with atypical breast lesions. The main outcome of this study is
breast cancer occurrence. Of the 2,938 patients with atypical breast lesions, 1,658 were documented to have received no
chemoprevention, and 184/1,658 (11.1 %) developed
breast cancer at a mean follow-up of 68 months. Estimated 10-year
cancer risks were 17.3 % with ADH, 20.7 % with ALH, 23.7 % with LCIS, and 26.0 % with severe ADH. In a subset of patients treated from 1999 on (the
chemoprevention era), those who received no
chemoprevention had an estimated 10-year
breast cancer risk of 21.3 %, whereas those treated with
chemoprevention had a 10-year risk of 7.5 % (p < 0.001).
Chemoprevention use significantly reduced
breast cancer risk for all atypia types (p < 0.05). The risk of
breast cancer with atypical breast lesions is substantial. Physicians should counsel patients with ADH, ALH, LCIS, and severe ADH about the benefit of
chemoprevention in decreasing their
breast cancer risk.