Associations of parity-related reproductive histories with ER± and HER2± receptor-specific breast cancer aetiology. (5th November 2016)

• Record Type: Journal Article
• Authors: Anderson, William F; Pfeiffer, Ruth M; Wohlfahrt, Jan; Ejlertsen, Bent; Jensen, Maj-Britt; Kroman, Niels
• Is Part Of: International journal of epidemiology. Volume 46:Number 1(2017)
• Page Start: 86
• Page End: 95
• Publication Date: 2016-11-05
• Subjects: breast cancer aetiology -- breast cancer subtype -- reproductive history -- oestrogen receptor -- human epidermal growth factor receptor-2; Epidemiology -- Periodicals; 614.4
• DOI: 10.1093/ije/dyw286
• Languages: English
• ISSNs: 0300-5771

Abstract

Abstract: Background: Associations of reproductive history with breast cancer risk differ by oestrogen receptor (ER±) status and possibly by the joint expression of ER and the human epidermal growth factor receptor-2 (ER±/HER2±). However, large sample sizes are needed to establish ER-specific risks by HER2± expression. Methods: We linked a cancer registry covering nearly 95% of the primary breast cancer diagnoses in Denmark with a research parity database to assess associations for parity, number of live births and age at first live birth (AFLB) with receptor-specific risk. Relative risks (RRs) for associations were estimated with Poisson regression models. Results: With nearly 31 million women-years of follow-up, 45 786 Danish women aged 20–84 years developed invasive breast cancer during 1992–2011. ER± expression was available for the entire study period and HER2± after 2006. Of the breast cancers with known ER expression, 79% were ER+. Most breast cancers with known ER and HER2 were HER2– (90% of ER+ cancers and 65% of ER– cancers). RRs differed by ER± expression for all reproductive variables ( p -homogeneity < 0.001). Associations were stronger for ER+ than ER– cancers and for those diagnosed before age 50. Parity and early [not later] AFLB showed a protective association with ER+/HER2– and risk association with ER–/HER2– cancers. Conclusion: Associations of reproductive history with breast cancer risk varied among Danish women by ER± and ER±/HER2± expression and age-at-diagnosis, consistent with receptor-specific and age-related etiological heterogeneity. Further stratification by HER2 status demonstrated dual (or opposite) effects for ER+/HER2– and ER–/HER2– cancers.