Background: Lesbian and bisexual women may be at greater risk of breast cancer than heterosexual women during the premenopausal period due to disparities in risk factors.
Methods: With 16 years of prospective data from a large cohort of U.S. women ages 25-58 years, we conducted a breast cancer risk assessment for 87,392 premenopausal women by applying the Rosner-Colditz biomathematical risk prediction model to estimate breast cancer risk based on known risk factors. On the basis of each woman's comprehensive risk factor profile, we calculated the predicted 1-year incidence rate (IR) per 100,000 person-years and estimated incidence rate ratios (IRR) and 95% confidence intervals (CI) for lesbian and bisexual women compared with heterosexual women.
Results: A total of 87,392 premenopausal women provided 1,091,871 person-years of data included in analyses. Mean predicted 1-year breast cancer IRs per 100,000 person-years for each sexual orientation group were heterosexual, 122.55; lesbian, 131.61; and bisexual, 131.72. IRs were significantly elevated in both lesbian (IRR, 1.06; 95% CI, 1.06-1.06) and bisexual (IRR, 1.10; 95% CI, 1.10-1.10) women compared with heterosexual women.
Conclusions: Our findings suggest that both lesbian and bisexual women have slightly elevated predicted breast cancer incidence compared with heterosexual women throughout the premenopausal period.
Impact: Health professionals must ensure that breast cancer prevention efforts are reaching these women. As more health systems around the country collect data on patient sexual orientation, the National Cancer Institute's SEER cancer registry should add this information to its data system to monitor progress in reducing sexual orientation-related disparities in cancer incidence and mortality.