Endometriosis and mammographic density measurements in the Nurses' Health Study II.

Abstract

Endometriosis and mammographic density have been hypothesized to be influenced by sex steroid hormonal exposures in adolescence and early adulthood. We investigated the association between endometriosis and mammographic density, a consistent and independent risk factor for breast cancer. We conducted a cross-sectional analysis among 1,581 pre- and postmenopausal women not previously diagnosed with breast cancer in the Nurses' Health Study II cohort. We measured average percent mammographic density and absolute dense and non-dense breast area using a validated computer-assisted method. Multivariable linear regression was used to estimate the association between endometriosis and mammographic density among pre- and postmenopausal women separately. Among premenopausal women, average percent mammographic density was 43.1% among women with endometriosis (n=91) and 40.5% among women without endometriosis (n=1,150). Endometriosis was not associated significantly with mammographic density among premenopausal (% difference=2.00 percentage points 95% CI -1.33, 5.33) or among postmenopausal women (% difference=-0.89 percentage points 95% CI -5.10, 3.33). Among premenopausal women, there was heterogeneity by BMI at age 18 (p value=0.003), with a suggested association among those who were lean at age 18 (BMI<20.6kg/m(2)) (% difference=3.74 percentage points 95% CI -0.29, 7.78). Endometriosis was not found to be associated with overall measurements of mammographic density.