Distinct Global Patterns and Trends in Lifetime Risk of Rectal Cancer Within Colorectal Cancer: A Population-Based Analysis from GLOBOCAN 2022

Background: Rectal cancer (RC) is traditionally grouped within colorectal cancer (CRC), despite growing evidence of distinct epidemiologic features. However, global comparative assessments of lifetime risks of RC relative to CRC remain limited. We aimed to estimate lifetime risks of developing and dying from RC and CRC worldwide and to examine geographic, socioeconomic, and temporal variations in the proportional contribution of RC within CRC. Methods: Age-specific incidence and mortality estimates for RC and CRC across 185 countries were obtained from GLOBOCAN 2022, together with population and all-cause mortality data from the United Nations. Lifetime risks of incidence (LRI) and mortality (LRM) were calculated using the adjusted-for-multiple-primaries (AMP) method by sex, country, region, and Human Development Index (HDI). The RC-to-CRC lifetime risk ratio quantified the proportional contribution of RC. Temporal trends were assessed in 42 countries using Cancer Incidence in Five Continents Plus (CI5plus) data and average annual percent change (AAPC). Results: In 2022, the global lifetime risk of developing RC was 1.61% and dying from RC was 0.95%, accounting for approximately 35% of the corresponding CRC lifetime burden (4.61% and 2.68%). Absolute lifetime risks of both RC and CRC increased with HDI. In contrast, the proportional contribution of RC varied markedly, peaking at 41%-43% in Central and South-Eastern Asia but falling below 20% in the Caribbean and Central America, and showed a negative association with HDI. The LRI/LRM ratio increased with socioeconomic development. Temporal analyses showed increasing LRI trends in 17 of 42 countries for CRC versus 9 for RC, while declines occurred in 14 countries for RC and 11 for CRC. Conclusions: RC constitutes a substantial yet epidemiologically distinct component of the global CRC burden. Its proportional contribution varies across regions and does not parallel absolute risk patterns, supporting the need for subsite-specific surveillance and prevention strategies.