Two decades of age-standardized rectal cancer incidence and its geographic disparities in Kazakhstan

Abstract Rectal cancer is a major global health challenge, with rising incidence in many regions and notable geographic disparities. This study aimed to analyze two decades of rectal cancer incidence in Kazakhstan, focusing on total case burden, age-standardized trends, sex differences, and geographic disparities. This retrospective population-based study included all newly diagnosed primary rectosigmoid junction and rectal cancer cases (incident ICD-10 C19-C20) among permanent residents of Kazakhstan diagnosed between 1 January 2005 and 31 December 2024, using national cancer registry data of the Republic of Kazakhstan. Crude and age-standardized incidence rates (ASR, WHO world standard) were calculated by sex, age group, and region. Temporal trends were assessed using joinpoint regression (annual percent change, APC; average annual percent change, AAPC). Spatial clustering was evaluated using Getis-Ord Gi* statistics across five predefined periods: pre-screening baseline (2005–2010), early screening implementation (2011–2013), post-implementation pre-pandemic (2014–2019), pandemic disruption (2020–2021), and post-pandemic period (2022–2024). Over the 20-year study period (2005–2024), a total of 28,368 rectal cancer cases were registered in Kazakhstan. Of these, 14,569 (51.4%) occurred in males and 13,799 (48.6%) in females. The vast majority of cases (88.1%) were diagnosed in individuals aged ≥ 50 years, with the highest case numbers observed at ages 65–69 years. Age-standardized incidence remained stable overall (AAPC + 0.2%, p = 0.376), with a persistent male predominance (ASR: males 10.9, females 7.0 per 100,000). Crude incidence increased significantly (AAPC + 1.2%, p < 0.001), and may be substantially influenced by population aging. Among individuals aged < 50 years, no significant full-period change was observed (AAPC − 0.3%, p = 0.553). Substantial regional disparities persisted after age standardization: the highest ASR was in Pavlodar region (12.7 per 100,000) and the lowest in Zhambyl region (4.7 per 100,000). ASR increased significantly in Atyrau (APC + 3.6%, p < 0.001), Kyzylorda (+ 2.3%, p = 0.006), and South Kazakhstan (+ 1.1%, p = 0.020), while it declined in Almaty city (− 1.8%, p < 0.001). Across all five periods, Getis-Ord Gi* yielded recurrent hot-spot classifications for Akmola, North Kazakhstan, and Astana and cold-spot classifications for South Kazakhstan and Kyzylorda, with confidence levels varying across periods. The same broad spatial structure was observed during 2020–2021. These findings are exploratory because only 16 spatial units and one spatial-weight specification were used. Over two decades, rectal cancer incidence in Kazakhstan remained age-dependent and male-predominant, with stable age-standardized rates but marked and persistent north-eastern geographic disparities unexplained by age structure alone. These findings support continued national and regional surveillance and further investigation of lifestyle, environmental, registry-quality, and healthcare-access determinants before geographically targeted prevention or cancer-control interventions can be recommended.