Abstract 1759: The association between alcohol, physical activity and breast cancer subtypes in a nested case-control study from the Norwegian Breast Cancer Screening Program
Authors: Ellingjord-Dale Merete , Vos Linda , Tretli Steinar , Hofvind Solveig , dos-Santos-Silva Isabel , Ursin Giske 
Published: July 2016

Abstract
Background:
Breast cancer (BC) is a complex disease, consisting of molecular subtypes with different prognosis and possibly different etiology. We and others have previously reported that hormonal factors such as hormone therapy and pregnancies predominantly affect luminal-like BC, but it is unclear whether alcohol and physical activity are associated only with certain subtypes.
Methods:
We conducted a case-control study nested within a cohort of 457,036 women who participated in the Norwegian Breast Cancer Screening Program (NBCSP) in 2006-2012, and who completed a questionnaire at baseline screening. In all, 5,554 BC cases with information on risk factors and hormone receptor status (i.e. estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor 2 (HER2) occurred during the follow-up. For each case, 5 controls were randomly selected from among participants who did not develop BC, frequency-matched to the cases on year of birth and year of screening. The following surrogate definitions of BC subtypes were used: ER+PR+HER2- (“luminal A-like”), ER+PR-HER2- (“luminal B-like, HER2 negative”), ER+HER2+ (“luminal B-like, HER2 positive”), ER-PR-HER2+ (“HER2 positive”) and ER-PR-HER2- (“triple negative”). We used multinomial logistic regression to estimate odds ratios (ORs), with 95% confidence intervals (CIs), adjusted for age, body mass index (BMI), education, age at menarche, number of pregnancies and menopausal status.
Results:
Weekly amount of alcohol intake was associated with an increased risk of BC overall (p for trend = 0.001). Analysis by subtype revealed a positive association between alcohol intake and BC risk for several subtypes, albeit it was statistically significant only for luminal A-like cancer. Compared to never drinkers, women who reported an alcohol intake &gt;6 glasses/week had a moderately increased risk of luminal A-like (OR = 1.41, 95% CI 1.14-1.73, p for trend = 0.0001), luminal B-like Her2 positive (OR = 1.55, 0.87-2.75) and triple negative BC (OR = 1.39, 0.81-2.37). In contrast, physical activity (low and high intensity exercise) was inversely associated with risk of breast cancer overall (p for trend = 0.002). Relative to women who reported doing no exercise, those who reported physical activity of ≥4 hours/week were at reduced risk for luminal-A like (OR = 0.76, 95% CI 0.63-1.01, p for trend = 0.01), luminal B-like Her2 positive (OR = 0.84, 0.46-1.54), and triple negative BC (OR = 0.80, 95% CI 0.45-1.44). The risk estimates for the other subtypes were close to 1.
Conclusions:
Alcohol intake was positively associated, and physical activity negatively associated, with BC overall. Although these associations were statistically significant only for luminal A-like BC, their direction and magnitude were rather similar across several subtypes.
Citation Format: Merete Ellingjord-Dale, Linda Vos, Steinar Tretli, Solveig Hofvind, Isabel dos-Santos-Silva, Giske Ursin. The association between alcohol, physical activity and breast cancer subtypes in a nested case-control study from the Norwegian Breast Cancer Screening Program. [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 1759.