Abstract B020: Early-onset colorectal cancer mortality trends and birth cohort effect in Mexico, 1998-2023

Introduction: In high-income countries, there is an increasing incidence of early-onset colorectal cancer (eoCRC; diagnosis before age 50) with individuals born recently facing higher risks relative to those born in the 1960s. In low- and middle-income countries (LMICs), eoCRC remains largely uncharacterized. In Mexico, in the last two decades, colorectal cancer (CRC) mortality has rapidly increased, becoming the leading cause of cancer mortality. Understanding epidemiologic patterns of eoCRC in this population may provide insights for early diagnosis and help generate hypotheses on etiologic factors. Thus, we aimed to describe trends in eoCRC mortality by sex and birth cohort. Methods: We obtained deaths between 1998 and 2023 for CRC (ICD-10 codes C18.0, C18.2-18.9, C19 & C20) from Mexico’s National Institute of Statistics and Geography. We used the National Population Council population estimates to calculate CRC mortality for ages 20 to 74 years by 5-year groups, stratified by ages 20-49 and 50-74, and sex. We estimated the average annual percent change (AAPC) in age-specific CRC mortality rates using joinpoint regression for 1998 to 2023. Age-period-cohort models were estimated to evaluate the effects of period and birth cohort by sex. Results: The age-standardized eoCRC mortality in 2023 was 2.1 (95% CI: 2.0, 2.3) per 100,000 in men and 1.7 (95% CI: 1.6, 1.9) for women. For older adults (aged 50-74), the corresponding estimates were 21.6 (95% CI: 20.8, 22.5) per 100,000 for men and 15.1 (95% CI: 14.4-15.8) for women. For eoCRC, increases in mortality were steepest for men and women aged 45-49 (AAPC: 3.1%; 95% CI: 2.3, 4.2 for men and 2.0%; 95% CI: 1.4, 2.9 for women). The corresponding estimates for men and women 65-69 years were 1.2% (95% CI: -1.5, 2.8) and -1.4% (95% CI: -4.7, 2.6). Men born in 1979 were 1.7 times (95% CI: 1.6-1.8) more likely to die of CRC, while women born in 1984 were 1.6 times (95% CI: 1.4-1.8) more likely, compared to their counterparts born in 1959. Conclusions: While absolute risk of eoCRC remains low, mortality is steadily rising in Mexico. Individuals born in the early 1980s faced a higher CRC mortality relative to those born in the early 1960s. Mexico should strengthen early diagnosis. Individuals born more recently may have been exposed to risk factors that were not present in earlier generations. Citation Format: Priscilla Espinosa-Tamez, Fernando Macías-González, Liliana Gómez-Flores-Ramos, Martin Lajous. Early-onset colorectal cancer mortality trends and birth cohort effect in Mexico, 1998-2023 [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: The Rise in Early-Onset Cancers—Knowledge Gaps and Research Opportunities; 2025 Dec 10-13; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(23_Suppl):Abstract nr B020.