ASPO Abstracts
Sedentary Time and Breast Cancer Risk in the Sister Study Cohort
Category: Lifestyles Behavior, Energy Balance & Chemoprevention
Conference Year: 2022
Abstract Body:
Purpose of the study: We investigated the association between sedentary time (ST) and breast cancer (BC) risk among women in the Sister Study, and explored possible differences by race/ethnicity, menopausal status at diagnosis, and estrogen receptor (ER) status. Methods: The Sister Study is a prospective cohort of 50,884 women aged 35-74 years who had no history of BC but had at least one sister with BC. ST was collected at the first detailed follow-up (~ 2 years after enrollment) and BC diagnoses (invasive and ductal carcinoma in situ) were reported annually. We used multivariable Cox proportional hazard regression to estimate the hazard ratios (HR) and 95% confidence intervals (CI) for the association of continuous ST (hours/day) and ST categories (<= 5 hours/day (referent), 6-9 hours/day, and >=10 hours/day) with BC diagnosed after first follow-up, with age as the primary time scale, adjusting for race/ethnicity, education, BMI, physical activity (MET hours/week), and number of pregnancies. Postmenopausal time was allowed a distinct baseline hazard by treating menopause as time-dependent. We explored effect measure modification by race/ethnicity and menopausal status at diagnosis. We used case-only multivariable logistic regression to examine etiologic heterogeneity by ER-negative versus ER-positive tumor types. Results: Among the 40,459 women included in this analysis, 35% reported 6-10 hours/day of ST, and 20% reported >= 10 hours/day of ST. ST (6-10 vs. <= 5 adjusted HR (aHR)=1.15 95% CI=1.05, 1.26; >= 10 vs. <= 5 aHR=1.12 95% CI=1.01, 1.25) was associated with increased BC risk. The association varied by menopausal status (p-heterogeneity<0.001), with hours spent in ST positively associated with postmenopausal BC (6-10 vs. <= 5 aHR=1.20 95% CI=1.10, 1.31; >= 10 vs. <= 5 aHR=1.26 95% CI=1.14, 1.39) and inversely associated with premenopausal BC (>= 10 vs. <= 5 aHR=0.74 95% CI=0.57, 0.95, p-trend 0.04). There was no difference in the HRs by race/ethnicity (p-heterogeneity=0.96). Among those who developed BC, ST (>= 10 vs. <= 5 aOR=1.22 95% CI=0.92, 1.62) was associated with increased odds for ER-negative relative to ER-positive disease. Conclusions: Increased ST was associated with increased risk of BC, especially post-menopause.
Keywords: Sedentary time, breast cancer, time spent sitting