Stress and risk of breast cancer; findings from a large population-based incident case-control study.

The relationship between stress and breast cancer (BC) remains a topic of debate. We investigated the association between stress experienced within the past year and the risk of BC. Population-based incident case-control study of 600 newly diagnosed BC cases and 600 population controls (18-75 years) recruited in Isfahan, Iran between 2021 and 2023. Logistic regression model with short-term stress as main exposure was used to estimate odds ratios (ORs) and 95% confidence intervals (CI) after adjusting for confounders. Multiplicative interaction was tested between stress and menopausal status as well as other confounders. One-year stress level was significantly associated with BC risk. Compared with women reporting low stress levels, the odds of BC were higher among those with high stress levels in both the unadjusted model (OR = 3.10, 95%Cl: 2.45-3.92) and the fully adjusted model (OR = 3.38; 95%CI (2.56, 4.47)). Based on the statistical test for multiplicative interaction, the association appeared stronger among premenopausal women (adjusted OR = 4.88, 95% CI: 3.17-7.52) than among postmenopausal women (adjusted OR = 2.34, 95% CI: 1.53-3.58), with evidence of interaction by menopausal status (p for interaction = 0.018). Despite the inherent limitations of case-control studies, including potential recall and selection biases, the findings of the current study suggest that higher levels of stress experienced within the past year may be associated with an increased risk of breast cancer, particularly among premenopausal women. Further prospective studies are warranted to clarify the nature and direction of this association.