The Association Between Volumetric Breast Density And Breast Cancer Subtypes Among Women Newly Diagnosed With Breast Cancer.

e13115 Background: Increased breast density is a strong risk factor for breast cancer, women with high breast density have a four to six-fold increased risk of breast cancer compared to those with low density. This study explores breast density as a risk factor for specific breast cancer subtypes in order to improve risk assessment and screening recommendations for the general population. Methods: 790 women ≥ 18 years with breast cancer were evaluated who had volumetric percent density and volumetric density grade (VDG) assessed from diagnostic mammograms obtained within 9 months of diagnosis. Breast cancer subtypes were approximated based on the estrogen receptor (ER), progesterone (PR) and Her2neu status; ER and/or PR positive/Her2 negative or positive (HR+), ER and PR negative and Her2 positive (Her2-positive) and ER, PR and Her2 negative (TN). A linear model on a log scale was conducted to evaluate the associations between percentage volumetric breast density and VDG and breast cancer subtypes and race. Results: 36% of women were < 50 years and 64% ≥50 years, 76% were white, 12% Black and 12% other race. There was no significant association between breast cancer subtype with age ( P = 0.068), BMI ( P = 0.81) or race ( P = 0.11). Women with VDG 1 or 2 were more likely to have HR+ (81.3%) than Her2-positive (5.1%) or TN subtypes (13.6%) (P = 0.024). There was no significant association between the percent volumetric breast density and breast tumor subtype or race. Conclusions: We found a significant association between lower breast density measured using VDG and the HR+ breast cancer subtype. This suggests a potential opportunity for assessing volumetric density grade for the development of individualized risk prediction models and for the identification of women who may benefit from preventive therapy to reduce HR+ breast cancer risk.