Breast cancer incidence in a cohort of women with benign breast disease from a multiethnic, primary health care population.

Women with benign breast diseases (BBD), particularly those with lesions classified as proliferative, have previously been reported to be at increased risk for subsequent development of breast cancer (BC). A cohort of 4970 women with biopsy-proven BBD, identified after histopathology review of BBD biopsies, was studied for determination of subsequent development of BC. We report on 4537 eligible women, 28% of whom are African-American, whose BBD mass was evaluable for pathologic assessment of breast tissue. Ascertainment of subsequent progression to BC from BBD was accomplished through examination of the tumor registries of the Henry Ford Health system, the Detroit SEER registry, and the State of Michigan cancer registry. Incidence rates (IR) are reported per 100,000 person years at risk (100 k pyr). Poisson regression models were used to evaluate the association of demographic and lesion characteristics with BC incidence, using person years at the time of BBD diagnosis as the offset variable. The estimated overall BC IR for this cohort is 452 (95% confidence interval [CI] = 394-519) per 100 k pyr. Incidence for women age 50 and older is 80% greater than for younger women (p = 0.007, IRR = 1.8, 95% CI = 1.36-2.36). Neither marital status (p = 0.91, IRR = 0.97, 95% CI = 0.73-1.29) nor race (p = 0.67, IRR = 0.9, 95% CI = 0.54-1.48) is associated with differences in BC IR. Compared with women having nonproliferative lesions, the risk for BC is greater for women with atypical ductal hyperplasia of (IRR = 5.0; 95%CI = 2.26-11.0; p < 0.001) and other proliferative lesions (IR = 1.7, 95% CI = 1.02-2.95; p = 0.04). BC risk for woman with atypical lesions is significantly higher than for women with proliferative lesions without atypia (IRR = 2.58, 95% CI = 1.35-4.90; p = 0.0039). Neither race nor marital status was a factor for BC incidence from BBD in this cohort. Age retained its importance as a predictor of risk. BBD lesion histopathology in the outcome categories of either proliferative without atypia or proliferative with atypia are significant risk factors for BC, even when adjusted for the influence of demographic characteristics. The risks associated with BBD histological classifications were not different across races.