Objective  To investigate the disparities in breast cancer burden and changing epidemiological trends between China and the United States (US) from 1990 to 2021 and identify the key driving factors.

Methods  The Global Burden of Disease database (1990-2021) was utilized to analyze breast cancer incidence, mortality, and disability adjusted life years (DALYs) in China and the US; we also assessed the associations with risk factors (e.g., obesity and smoking) through regression models and spatiotemporal analysis.

Results China’s breast cancer age-standardized incidence rate (ASIR) surged from 9.08/100,000 in 1990 to 19.36/100,000 in 2021, whereas the US ASIR declined from 44.37/100,000 to 37.49/100,000. Regarding the age-standardized mortality rate (ASMR), China saw a marginal reduction from 4.70/100,000 to 4.40/100,000, whereas the US experienced a significant decline from 13.03/100,000 to 9.28/100,000, narrowing the mortality gap from 2.8-fold to 2.1-fold. Key risk factors contributing to mortality and DALYs included smoking, exposure to secondhand smoke, low physical activity, high red meat and alcohol intake, elevated fasting blood glucose levels, and high body mass index. The rising cancer incidence in China is associated with the westernization of lifestyles and changes in fertility patterns, whereas the United States has achieved a dual decline in both incidence and mortality rates through widespread screening and control of hormone replacement therapy.

Conclusions Both the incidence and mortality rates of breast cancer in China rank among the highest globally, with incidence rates still increasing, indicating severe issues in prevention and control. In contrast, although the incidence rate in the US is higher than that in China, it shows a declining trend. To alleviate the growing burden of breast cancer, China must further enhance the intensity and coverage of breast cancer screening.