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Large prospective studies in high-income countries have enabled the estimation of preventable cancer cases, guiding cancer control strategies. With breast cancer incidence rising rapidly in Malaysia, there is an urgent need for locally relevant data to inform effective prevention and control measures. We quantified the population-level contribution of risk factors in Malaysia using population-specific prevalence and literature-based relative risks.

We calculated population attributable risk using: (1) Malaysia-specific prevalence from national surveys and local epidemiological studies and (2) relative risks derived from meta-analyses of Asian prospective cohorts or case-control studies. We estimated attributable proportions using Levin's formula, adjusted for the joint effects of risk factors with a multiplicative model, and generated simulation-based confidence intervals to quantify their impact on overall disease burden.

Mammographic density (MD) accounted for 32.8% of breast cancer burden in Malaysian women, followed by modifiable risk factors-elevated body mass index (BMI, 14.7%) and passive smoking (8%). Family history and genetic factors collectively contributed 12.1%. Reproductive factors play a pronounced role before menopause, whereas BMI predominate after menopause. Their impact varies across ethnic groups: MD was most influential among Chinese women, while elevated BMI played a greater role among Malays and Indians.

A notable proportion of the breast cancer burden in Malaysia may be attributable to lifestyle and reproductive factors, while genetic susceptibility and MD also contribute importantly to disease burden. These findings support a balanced approach to breast cancer control, combining targeted prevention with risk-based early detection tailored to age and ethnic differences.