Allostatic load and risk of invasive breast cancer among postmenopausal women in the U.S.

Objective: Allostatic load can reflect the body's response to chronic stress. However, little is known about the association between allostatic load and risk of breast cancer in postmenopausal women. This study used a large prospective cohort in the United States to examine the relationship between allostatic load and invasive breast cancer risk, and to evaluate the relationship by racial and ethnic identity and breast cancer subtypes. Methods: Among 161,808 postmenopausal participants in Women's Health Initiative, eligible were a subsample of 27,393 postmenopausal women aged 50–79 years old, who enrolled from 1993 to 1998, had serum test biomarkers, and were followed for breast cancer incidence through February 2022. Allostatic load at enrollment was computed based on eight biomarkers from lab serum tests and a questionnaire about participants' prescription drug use. The associations between allostatic scores and risk of breast cancer (overall and by subtypes) were assessed using Cox proportional hazards models. The race and ethnic differences were examined. Results: Over a median follow-up time of 17.24 years, 1722 invasive breast cancer cases were identified. High allostatic load was associated with an increased risk of breast cancer (HR = 1.36, 95%CI: 1.20, 1.54 for third tertile vs first tertile, P_trend < 0.0001). Similar trends were found in White women and non-Hispanic women. Higher allostatic load was associated with hormone receptor-positive and HER2/Neu-negative breast cancer (HR = 1.54, 95%CI: 1.30, 1.80 for third tertile vs first tertile, P_trend < 0.0001). Conclusion: In this study, we found that higher allostatic load was significantly associated with an increased risk of breast cancer in postmenopausal women.