Trajectories in mammographic breast screening participation in middle-age overweight and obese women: a retrospective cohort study using linked data

Objectives: Despite the established benefits and availability of mammographic breast screening, participation rates remain suboptimal. Women with higher BMIs may not screen regularly, despite being at increased risk of postmenopausal breast cancer and worse outcomes. This study investigated the association between prospective changes in BMI and longitudinal adherence to mammographic screening among women with overweight or obesity. Methods: Retrospective cohort study of women (N = 2822) participating in the Australian Longitudinal Study on Women's Health with an average follow-up of 20 years, with screening participation enumerated via BreastScreen NSW, Australia clinical records over the period 1996-2016. Association between BMI and subsequent adherence to screening was investigated in a series of marginal structural models, incorporating a time variant/invariant socio-demographic, clinical, and health behaviour confounders. Models were also stratified by a proxy measure of socio-economic status (education). Results: Participants with overweight/obesity were less adherent to mammography screening, compared to healthy/underweight participants (OR=1.29, 95 % CI=1.07, 1.55). The association between overweight/obesity and non-adherence was higher among those who ever had private health insurance (OR=1.30, 95 % CI=1.05, 1.61) compared to those who never had private health insurance and among those with lower educational background (OR=1.38, 95 % CI=1.08, 1.75) compared to those with higher educational background. Conclusions: Long-term impacts on screening participation exist among women with higher BMI, who are less likely to participate in routinely organised breast screening. Women with a higher BMI should be a focus of efforts to improve breast screening participation, particularly given their increased risk of breast cancer and association of higher BMI with worse breast cancer outcomes among older women.