ASPO Abstracts
Impact of family history risk score on associations between breast cancer and physical activity in adulthood
Category: Lifestyles Behavior, Energy Balance & Chemoprevention, Lifestyles Behavior, Energy Balance & Chemoprevention
Conference Year: 2018
Abstract Body:
Background: Recreational physical activity has been consistently associated with a reduced breast cancer risk in women overall. Less is known about the impact of a family history of breast cancer on this association. This is an important consideration because extent of family history differentially affects risk for breast cancer and associations with other breast cancer risk factors have been shown to vary by family history. Methods: The Sister Study is a prospective cohort of 50,884 women who each had a sister who was diagnosed with breast cancer, but did not have breast cancer themselves at baseline. Women reported their sport/exercise activities during the 12 months before enrollment. Average hours/week and MET-hours/week were considered in association with breast cancer overall and by estrogen receptor (ER) status. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated with Cox regression. Extent of family history was characterized by a novel Bayesian score incorporating the population hazard function, family size, and number of breast cancer cases and age at diagnosis in first-degree female relatives. Modification by extent of family history was evaluated in stratified analyses with an interaction term between risk score and physical activity. Results: During follow-up (mean=8.3 yrs), 3,053 breast cancer cases were diagnosed. Participation in 7 compared to <1 hour/week of physical activity was associated with lower breast cancer risk overall (HR=0.85; 95%CI: 0.74-0.98). Inverse associations were evident for ER+ tumors (HR=0.84; 95%CI: 0.71-0.98), but not ER-. Family history risk score modified physical activity and overall breast cancer associations. Among those with low risk scores, 7 hours/week of physical activity was associated with a HR of 0.78 (95%CI: 0.63-0.97), compared to a HR of 1.06 among women with high risk scores (95%CI: 0.88-1.22). Conclusions: Overall findings suggest that physical activity is beneficial in lowering breast cancer risk, even in women with a family history of breast cancer. The amount of benefit appears to vary with degree of familial risk. Nonetheless, women with a family history may have a heightened concern about their own risk, so becoming or remaining active may be a positive step they can undertake.
Keywords: physical activity; family history; breast cancer