S694 Conflicting Trends in the Incidence of Rectal Cancer Among Young vs Old Adults in the United States and Establishing a Predictive Model to 2030

Introduction: Despite ongoing efforts in screening and awareness, recent reports confirm a rising trend in colon cancer among young adults, while incidence has declined among older adults in the U.S. This study investigates rectal cancer incidence from 2001 to 2021 and projects future trends to 2030. Methods: We analyzed data from the United States Cancer Statistics (USCS), compiled by the CDC and NCI, for adults aged 20–49 and ≥50 years, stratified by sex. Age-adjusted incidence rates per 100,000 were calculated. Joinpoint regression estimated annual percent change (APC) and average annual percent change (AAPC) where appropriate. Using RStudio, we built an ARIMA time series model to forecast 2030 incidence. Model performance was assessed using the Ljung-Box test, RMSE, and Augmented Dickey-Fuller test. Results: Between 2001 and 2021, the incidence of rectal cancer among young adults aged 20-49 rose from 2.78 to 4.54 per 100,000 (APC: 2.10, P < 0.05), with similar trends in men (3.12 to 5.14, APC: 2.12, P < 0.05) and women (2.46 to 3.94, APC: 2.06, P < 0.05). The predictive models estimate that by 2030, the age-adjusted incidence among young adults will reach 4.99 per 100,000, 5.64 for men, and 4.37 for women. Meanwhile, among adults aged 50+, the incidence dropped from 32.85 in 2001 to 25.81 in 2011 (APC: 2.39, P < 0.01) and to 24.25 in 2021 (APC: 0.92, P = 0.011; AAPC: 1.66, P < 0.01). Among men, the rate fell from 43.77 in 2001 to 34.23 in 2010 (APC: 2.65, P < 0.01), and to 30.90 by 2021 (APC: 1.22, P < 0.01; AAPC: 1.87, P < 0.01). For women, it declined from 24.42 in 2001 to 19.34 in 2011 (APC: 2.42, P < 0.01) and 18.54 in 2021 (APC: 0.73, P = 0.043; AAPC: 1.59, P < 0.01). By 2030, incidence among adults 50+ is projected to fall to 18.33 per 100,000, 22.48 for men, and 14.37 for women. Conclusion: Our study identifies that there is an increasing trend in rectal cancer among young adults. We encourage the reevaluation of the current guidelines to incorporate earlier and more frequent screening.