Endometriosis and Mammographic Density Measurements in the Nurses’ Health Study II

Abstract

Purpose

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.

Methods

We conducted a cross-sectional analysis among 1,581 pre- and post-menopausal 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.

Results

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 pre-menopausal (% difference=2.00 percentage points 95% CI:(−1.33,5.33)) or among post-menopausal 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< 20.6 kg/m ²) (% difference=3.74 percentage points 95% CI:(−0.29,7.78)).

Conclusion

Endometriosis was not found to be associated with overall measurements of mammographic density.