ASPO Abstracts

Adolescent physical activity and breast cancer risk before age 50 years: findings from the Prospective Family Study Cohort (ProF-SC)

Authors: Kehm RD, Genkinger JM, MacInnis RJ, John EM, Phillips KA, Knight JA, Milne RL, Colonna SV, Chung WK, Kurian AW, Andrulis IL, Buys SS, Daly MB, Hopper JL, Terry MB

Category: Lifestyles Behavior, Energy Balance & Chemoprevention
Conference Year: 2021

Abstract Body:
Purpose of the study: We previously found that physical activity in adulthood is associated with reduced risk of breast cancer (BC) for women across the spectrum of absolute BC risk, including women under age 50 years and those with BRCA1 and BRCA2 pathogenic variants. In this study, we evaluated the impact of adolescent physical activity on BC risk before age 50 years. Methods: We used data from the Prospective Family Study Cohort (ProF-SC), which is enriched for BC family history. Women reported by baseline questionnaire their average levels of moderate and strenuous physical activity during adolescences (12-17 years), which we converted to total metabolic equivalents and categorized into quintiles after adjusting for baseline age. We conducted attained age analyses until 50 years using multivariable Cox proportional hazards regression to evaluate associations in 19,499 women (1,532 with BRCA1 and BRCA2 pathogenic variants) who were enrolled within 2 years of their first primary BC diagnosis or had no personal history of BC at baseline (pseudo-incident cohort). Results: There were 3,033 women (424 with BRCA1 and BRCA2 pathogenic variants) diagnosed with BC before age 50 years in the pseudo-incident cohort (50% estrogen receptor (ER)+, 28% ER-, 22% missing ER status). In models stratified by decade of birth and adjusted for race/ethnicity, education, and study center, women in the highest versus lowest quintile of age-adjusted adolescent physical activity had a 15% reduced risk of BC before age 50 years (HR=0.85, 95% CI=0.75-0.95; p-trend=0.046). Adolescent physical activity was associated with ER+ BC (Q5 vs. Q1: HR=0.83, 95% CI=0.70-0.98; p=0.045), but not ER- BC (HR=0.91, 95% CI=0.71-1.14; p-trend=0.686). Adolescent physical activity was not associated with BC risk before age 50 years for women in the pseudo-incident cohort with BRCA1 and BRCA2 pathogenic variants, but an association was found when we restricted to those affected with BC before baseline (n=726; HR=0.64, 95% CI=0.45-0.91; p-trend=0.042). Conclusion: Unlike the association we previously found for adult physical activity and BC risk, which was observed irrespective of ER status, the association of adolescent physical activity with BC risk before age 50 years appears to be specific to ER+ BC.

Keywords: premenopausal breast cancer risk, adolescent physical activity, BRCA1 and BRCA2 pathogenic variants