Temporal trends and population disparities in breast cancer mortality in China (2004–2021): a joinpoint regression analysis of national surveillance data

Background Breast cancer is a major malignancy threatening women’s health. Understanding the long-term trends of breast cancer mortality in China and the disparities across different populations is crucial for developing targeted prevention and control strategies. This study aimed to assess the long-term trends of breast cancer mortality among adult women in China from 2004 to 2021 and to examine differences by age, urban-rural status, and geographic region. Methods This study used data from the national Disease Surveillance Points (DSP) system, including breast cancer death records among women aged 20 years and older from 2004 to 2021. The study covered a cumulative surveillance population of 1,163,902,200 person-years among women and included 108,048 reported breast cancer deaths. Crude mortality rates and age-standardized mortality rates (ASMR) were calculated. Joinpoint regression analysis was applied to evaluate long-term trends in ASMR and the annual percent change (APC). An age-period-cohort model was also constructed to assess the independent effects of age, period, and birth cohort on breast cancer mortality, estimating relative risks (RRs) and 95% confidence intervals to characterize mortality risk across age groups, periods, and birth cohorts. A sensitivity analysis was conducted by stratifying the study period into pre-expansion (2004–2012) and post-expansion (2013–2021) periods to assess the potential influence of DSP system expansion on observed mortality trends. Results From 2004 to 2021, the DSP system recorded 108,048 breast cancer deaths among women aged ≥ 20 years, representing a cumulative surveillance population of 1,163,902,200 person-years. The crude mortality rate increased from 7.9 per 100,000 in 2004 to 10.2 per 100,000 in 2021, while ASMR decreased from 6.5 to 5.9 per 100,000. Joinpoint regression indicated a non-significant downward trend in ASMR over the study period (APC = -0.41, 95% CI: -1.11 to 0.33, P = 0.246), with no significant joinpoints observed. Mortality differences persisted between urban and rural areas, with urban regions consistently higher than rural regions, and between regions, with higher mortality in the eastern and central regions compared to the western region. Age-period-cohort analysis showed that age had the strongest effect on mortality risk, with risk increasing steadily with age; period effects were relatively stable, and birth cohort effects showed an overall declining trend. Conclusions From 2004 to 2021, age-standardized breast cancer mortality among Chinese women showed a gradual decline, while disparities by age, urban-rural status, and region persisted. Continued monitoring and targeted prevention efforts focusing on high-risk populations and high-burden regions are warranted to reduce breast cancer mortality and related health inequities.