Association between risk-related lifestyle factors, screening adherence and breast cancer incidence: a decomposition analysis

Adherence to breast cancer (BC) screening may have mediated the association between lifestyle-related risk factors and BC incidence, but evidence on this hypothesis remains limited. This study aimed to decompose the overall effects of lifestyle factors on BC incidence, considering the mediating effect of screening adherence. In this longitudinal cohort study with follow-up from 2001 (cohort age: 50-55) to 2019 (cohort age: 68-73), we used a four-way decomposition approach to break down the overall effect of lifestyle factors on BC incidence into direct effects and mediated effects through screening adherence to quantify their total excess risk ratios (TERRs). Of the 10,579 women included in the study, 5.40% (n = 571) were diagnosed with BC during follow-up, with a higher proportion among those who adhered to BC screening (5.83%, n = 474) than non-adherers (3.96%, n = 97). The overall increased risk of BC was observed for higher body mass index (BMI) (TERR = 1.30), alcohol consumption (TERR = 1.55), and hormone replacement therapy (HRT) use (TERR = 1.57) (all P < 0.0001). The direct effects remained significant for BMI (excess relative risk [ERR] = 0.37, p = 0.001), alcohol consumption (ERR = 0.44, p = 0.003), and oral contraceptive use (ERR = - 0.69, p < 0.001) after adjusting for the mediation effect of screening. Significant indirect effects were also observed for alcohol consumption (3.32%, p = 0.001) and HRT use (5.08%, p < 0.001). These findings underscore the complex nature of BC risk and highlight the importance of considering both lifestyle factors and screening in cancer prevention strategies.