Breast Cancer in Kazakhstan, 2004–2023: Successful Mortality Reduction Driven by Organized Screening and Stage Shift

OBJECTIVE: To quantify two-decade national trends in the breast cancer burden in Kazakhstan and evaluate the performance of the organized mammography screening programme-including stage distribution and regional heterogeneity after its scale-up. METHODS: We conducted a retrospective, population-based evaluation using national registry and screening data. Population indicators (incidence, mortality, years of potential life lost) were analysed for 2004-2023; screening performance (coverage, abnormal rate, cancer detection rate, positive predictive value, benign biopsy rate, number needed to screen, programme contribution) was assessed for 2010-2023. Trends were modelled with Joinpoint; staging followed TNM (I-II "early", III-IV "advanced"). RESULTS: ASIR increased from 39. 3 per 100, 000 women in 2004 to 54. 4 in 2023 (with a transient dip to 44. 9 in 2020), whereas ASMR declined from 16. 6 to 10. 2 per 100, 000 over the same interval; the mortality-to-incidence ratio decreased from 0. 42 to 0. 19. YPLL₇5 fell from 175. 1 per 100, 000 in 2004 to a nadir of 76. 0 in 2018, then measured 104. 9 in 2023. The proportion diagnosed at stages I-II rose from 71. 1% (2010) to 88. 6% (2023), with corresponding declines in stage III (22. 2% → 8. 7%) and stage IV (6. 8% → 5. 1%). Following the expansion of eligibility to ages 40-70 (from 2018), screening throughput and coverage increased, but performance remained heterogeneous across regions, with variability in recall rates, detection yield, and downstream diagnostic pathways. CONCLUSION: Across 2004-2023, Kazakhstan experienced a favourable divergence between rising incidence and falling mortality, substantial reductions in premature mortality, and a marked shift toward earlier-stage diagnosis. These gains coincide with the maturation of the organised screening programme and broader system improvements. Consolidation will require targeted, region-specific quality-improvement bundles and resilience strategies to protect screening coverage and diagnostic capacity during system shocks.