Abstract 870: Analysis of breast cancer risk factors by expression of tumor markers: results of 34 studies in the Breast Cancer Association Consortium (BCAC)
Authors: Yang Xiaohong (Rose) , Chang-Claude Jenny , Goode Ellen , Couch Fergus , Nevanlinna Heli , Milne Roger , Gaudet Mia , Schmidt Marjanka , Spurdle Amanda , Fasching Peter , Humphreys Manjeet , Easton Douglas , Pharoah Paul , Sherman Mark , Garcia-Closas Montserrat 
Published: February 2011

Abstract
Epidemiologic studies suggest that breast cancer risk factor associations vary by tumor marker expression; however, individual studies have had limited power to address this question. We pooled data from up to 35,568 invasive breast cancer cases from 34 studies participating in the Breast Cancer Association Consortium (BCAC) to evaluate associations between established risk factors (age at menarche, nulliparity, age at first full time birth [AFFTB], body mass index [BMI] and family history) and breast cancer subtypes, defined by immunohistochemical expression of ER, PR, HER2, and basal markers (CK5/6 or CK5, EGFR). We used polychotomous logistic regression to evaluate relationships between risk factors and tumor subtypes in case-only analyses and to estimate case-control odds ratios and 95% confidence intervals for the associations between risk factors and specific tumor subtypes in 11 population-based studies including up to 12,841 cases and 17,032 controls. In case-only analyses, we found that reproductive risk factors were more common in hormone receptor positive tumors: early age at menarche was most strongly related to PR status (34.6% vs. 32.4% of women with age at menarche ≤12 years among PR+ and PR- cases, respectively, P= 0.001); whereas nulliparity, and late AFFTB in parous women were most strongly related to ER status (15.3% vs. 13.6% nulliparous women, 17.1% vs. 15.2% women with late AFFTB [≥30 years], among ER+ and ER- cases, respectively, P=2.6×10−6 for nulliparity and P=2.0×10−7 for late AFFTB). Nulliparity and late AFFTB were less common among triple negative (TN) tumors overall and among TN tumors expressing basal markers. Elevated BMI in women aged 50 years or younger was more common in ER-&PR- than ER+&PR+ tumors (17.0% vs 13.6% women with BMI ≥30, respectively, P=1.3×10−7), whereas above age 50 years, elevated BMI was more common in ER+&PR+ than ER+&PR- tumors (20.9% vs 16.7% women with BMI ≥30, respectively, P=2.8×10−8 comparing BMI ≥30 to BMI &lt;25). In case-control analyses, early age at menarche was associated with increased risk of PR+ tumors; nulliparity and late AFFTB were most strongly associated with increased risk of (ER+ or PR+)&HER2- tumors, and did not increase the risk of TN tumors. Having a family history of breast cancer increased the risk of all tumor subtypes, although the association was strongest for TN tumors expressing basal markers. Our data provide convincing evidence for etiological heterogeneity with respect to breast cancer risk factors stratified by ER and PR status. Stratification by additional markers provides additional insights about etiologic differences in breast cancer risk.
Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 870.