A Large Cohort Study of Height and Mammographic Density in Relation to Breast Cancer Risk among Korean Women

Background: Height and mammographic breast density are well-known risk factors for breast cancer. This study aims to investigate the association between height and mammographic density with breast cancer risk in a large population-based cohort of Korean women. Methods: This retrospective cohort study included 4,851,115 women ages 40 and older who underwent screening mammography through the Korean National Cancer Screening Program between 2009 and 2014 and were followed up until 2016. Multivariable Cox proportional hazard models were used to estimate adjusted HRs and 95% confidence intervals (CI) for the associations among height, mammographic density, and breast cancer risk. Results: A taller stature was associated with an increased risk of breast cancer, with women in the highest quintile of height (Q5) having a 1.54-fold (95% CI, 1.49-1.59) greater risk than those in the lowest quintile (Q1). When analyzing breast cancer risk based on height and mammographic density, women in the highest quintile for height (Q5) with extremely dense breasts had a 4.51-fold (95% CI, 4.24-4.79) greater risk than those in the lowest quintile (Q1) with almost entirely fatty breasts (Ptrend < 0.001). Conclusions: This first study to simultaneously examine these two variables found that height and mammographic density were independently associated with breast cancer risk in this large cohort of Korean women. Impact: Height and mammographic density can help stratify risk in screening populations for breast cancer. Careful consideration of screening strategies may be beneficial for taller women with dense breasts.