Abstract 4345: Association of smoking with breast cancer risk by estrogen and progesterone receptor status: the multiethnic cohort
Authors: Gram Inger T. , Park Song-Yi , Kolonel Laurence N. , Maskarinec Gertraud , Wilkens Lynne R. , Haiman Christopher , Le Marchand Loic 
Published: July 2016

Abstract
Background: The 2014 report of the Surgeon General put forward seven major summary points for the smoking and breast cancer relationship that needed to be addressed. One of these was that there was insufficient evidence to conclude that the risk of breast cancer from smoking differs between women diagnosed with ER+ tumors and those diagnosed with ER-tumors. The purpose of the present study was to examine whether the previously-reported association between risk of breast cancer and smoking in the Multiethnic Cohort (MEC) differed by ER+, ER-, PR+ or PR-tumor status.
Methods: From 1993 to 2010, we followed 83,300 women who were enrolled in the MEC at 45-75 years of age. We identified cancer cases via linkages to the statewide Hawaii and California cancer registries through December 2010. We used Cox proportional hazards regression with age as the underlying time scale to estimate multivariate-adjusted hazard ratios (HR) and 95% confidence intervals (CI) for the associations between different measures of smoking exposure and the four types of tumors according to hormone receptor status. The included covariates were selected a priori. For parous women, we also estimated breast cancer risk by category
of age at smoking initiation in relation to first childbirth (after or within 1 year before first childbirth, 1-5 years before, or &gt;5 years before) compared with parous never smokers for each tumor type.
Results: At cohort entry, the mean age of the participants was 62 years. Of these women, 45% reported at baseline that they had ever smoked. During a mean follow-up of 15 years, 4,484 women developed invasive breast cancer of which 2,417 (53.9%) had known status for at least one hormone tumor receptor. Altogether, 1,939 women were diagnosed with ER+, 469 with ER-, 1,548 with PR + and 688 with PR- hormone receptor status. The HRs associated with ever versus never smoking were similar for the tumor subtypes: ER+(1.05, 95% CI: 0.95, 1.15), ER-(0.99, 95% CI: 0.82, 1.20), PR+ (1.06, 95% CI: 0.96, 1.18), PR- (1.00, 95% CI: 0.85, 1.17). Compared with never smokers, ever smokers who had smoked more than 20 pack-years had a 17% a higher risk of ER+ (1.17, 95% CI 1.01-1.35) and an 11% higher risk of ER- (1.11, 95% CI 0.83-1.49) breast cancer.
Among parous women, those who had smoked more than 5 years before their first live childbirth had an increased risk of ER+ breast cancer of 45% (95% CI 1.18-1.77) and a non-statistically significant increase for ER- breast cancer of 13% (95% CI 0.72-1.76) than never smokers. The respective values for women with PR+ and PR- tumors were 37% (95% CI 1.09-1.73) and 43% (95% CI 1.03-2.01).
Conclusions: Parous women who had smoked more than five years before their first childbirth seem to have the most noticeable risk regardless of tumor type. The current data do not support any difference for the smoking and breast cancer association by hormone receptor status although this may be due to lack of power.
Citation Format: Inger T. Gram, Song-Yi Park, Laurence N. Kolonel, Gertraud Maskarinec, Lynne R. Wilkens, Christopher Haiman, Loic Le Marchand. Association of smoking with breast cancer risk by estrogen and progesterone receptor status: the multiethnic cohort. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4345.