Abstract P6-10-10: Association between mammographic density and breast cancer subtypes among Chinese women
Authors: Yang XR , Li J , Li E-N , Guida JL , Li M , Sung H , Lu N , Hu N , Gierach GL 
Published: May 2016

Abstract
Epidemiological studies have shown that associations between breast cancer risk and risk factors vary by tumor pathology such as estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) status. Mammographic density (MD) is a strong risk factor for breast cancer, but data on the association between MD and breast cancer subtypes have been inconsistent and most studies have been conducted among Western women. The goal of this study was to evaluate the association between MD and breast cancer subtypes in an Asian population where the proportion of dense breast tissue is higher but the overall breast cancer incidence rate is much lower compared with Western countries. Breast cancer cases from a cancer hospital in Beijing, China with MD and ER, PR, and HER2 immunohistochemical (IHC) data were included in this analysis. To reduce subtype misclassification, we excluded cases that were HER2 2+ for IHC but had no FISH data. Tumor subtypes were defined as Luminal A (ER+ or PR+ and HER2-, N=376), Luminal B (ER+ or PR+ and HER2+, N=97), HER2-overexpressing (ER- and PR- and HER2+, N=71), and triple negative (TN, ER- and PR- and HER2-, N=66). MD was assessed on digital mammograms and categorized into four levels using the Breast Imaging Reporting and Data System (BI-RADS) scoring system (a=almost entirely fat, b=scattered fibroglandular densities, c=heterogeneously dense, and d=extremely dense). Because there were few cases with almost entirely fat breasts, we combined MD levels "a" and "b" as our reference group. Polychotomous logistic regression was used to assess the association between MD and breast cancer subtypes with the adjustment of age, menopausal status, parity, age at menarche, and body mass index (BMI) since all these variables showed significant inverse associations with MD (P=0.002 for age at menarche and P&lt;0.0001 for all others). Compared with luminal A cases, cases with HER2-overexpressing tumors were significantly more likely to have extremely dense breasts (Odds ratio [OR], 2.6; 95% confidence interval [CI], 1.2-5.7). Cases with luminal B (OR, 2.1, 95% CI, 1.2-3.9) and TN (OR, 2.9, 95% CI, 1.5-5.8) tumors had significantly higher proportions of heterogeneously dense but not extremely dense tissue compared with luminal A cases. Our data suggest that higher MD is associated with more aggressive tumor subtypes, particularly the HER2-overexpressing subtype among Chinese breast cancer cases. If confirmed in larger studies, these results may provide insight into the higher incidence rates of HER2-overexpressing breast cancer seen among young Asian American and Asian women.
Citation Format: Yang XR, Li J, Li E-N, Guida JL, Li M, Sung H, Lu N, Hu N, Gierach GL. Association between mammographic density and breast cancer subtypes among Chinese women. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-10-10.