Lifecourse growth and development determinants of mammographic density in Black women.

Background: High mammographic density is one of the strongest breast cancer risk factors; however, determinants of high mammographic density are understudied in Black women. We assessed growth and development factors across the lifecourse in relation to mammographic density.

Methods: Within the Black Women's Health Study (BWHS), we used Cumulus software to assess percent mammographic density from digital screening mammograms for 5,905 women ages 40-74. We fit linear regression models to quantify the association of lifecourse characteristics including birth weight, childhood somatotype, age at menarche, body mass index (BMI) at age 18, height, BMI at mammography, and adulthood waist-to-hip ratio with density overall and by age. We also performed a path analysis to assess the total and mediating effects of the growth and development factors on density.

Results: BMI at age 18, height, BMI at mammography, and waist-to-hip ratio were significantly and inversely associated with density. On path analysis, total effects of childhood somatotype (standardized  = -0.05, p <0.001), BMI at age 18 (standardized  = -0.13, p <0.001), BMI at mammography (standardized  = -0.22, p <0.001), and waist-to-hip ratio (standardized  = -0.04, p <0.001) were associated with density.

Conclusions: Several factors across the lifecourse - greater childhood somatotype, BMI at age 18, height, BMI at mammography, and waist-to-hip ratio - were associated with lower mammographic density in this cohort of Black women.

Impact: Body size closer to the time of mammography may be more meaningful in determining mammographic density, though early life adiposity also influences mammographic density.