Abstract PO-191: Distinct patterns of early-onset colorectal cancer among Nigerians and African Americans: An international cohort study (2020)

Abstract Colorectal cancer incidence rates are rising among individuals age younger than 50 years (early-onset CRC) globally with causes unknown. Racial and ethnic disparities in early-onset CRC have also grown more pronounced, as blacks have higher early- onset CRC incidence and poorer survival compared with whites. We described the prevalence and burden of early-onset CRC among Africans in Nigeria and African Americans in the United States. We identified black individuals diagnosed with a first primary colorectal cancer ages 18 to 49 years between 1989 and 2017 at Ahmadu Bello University Teaching Hospital in Zaria, Nigeria using the Zaria Cancer Registry (Nigerians), and from population-based cancer registries across the US (African Americans) using the NIH/NCI’s Surveillance, Epidemiology, and End Results (SEER) program. Multivariable logistic regression models were used to investigate clinicopathologic and demographic differences between Nigerians and African Americans with early-onset CRC adjusted for age, sex, tumor site and grade. A total 566 and 31,284 colorectal adenocarcinoma cases were diagnosed among Nigerians and African Americans, respectively, in hospitals and clinics over the 28-year study period. More than 60% of Nigerian patients (n=354) were diagnosed with early-onset CRC. In contrast, one out of every 8 (12.5%) African Americans were diagnosed with CRC before age 50 years (n=3,898; P&amp;lt;0.0001). Subsequent analyses focused on the subset of this population diagnosed with early-onset CRC, which included 4,252 black individuals (354 Nigerian and 3,898 African American patients). Overall, approximately one-third of young black patients were diagnosed with rectal tumors (30.8%). Nigerians with early-onset CRC were more likely to be male compared to African American patients (57.9% vs 49.1%; P=0.001). Among African Americans, one quarter of early-onset cases were diagnosed with cancers of the rectum (26.5%), whereas 77.4% of young Nigerian patients were diagnosed with rectal tumors (P&amp;lt;0.0001). Nigerian individuals with early-onset CRC were 10-fold more likely to be diagnosed with rectal cancers (OR=10.35, 95%CI=7.14-14.99, P&amp;lt;0.001) and more likely to be diagnosed at younger ages (OR=0.87, 95%CI=0.85-0.89, P&amp;lt;0.001) compared with young African Americans. Young Nigerians with CRC were also 61% less likely to be diagnosed with high-grade (grade III/IV) tumors compared to African Americans with early-onset CRC (OR 0.39, 95%CI 0.23-0.67, P=0.001). This international cohort study reveals distinct patterns of early-onset CRC among black patients, as Nigerians were more likely to be diagnosed with rectal tumors and at younger ages compared with African Americans. Further investigation of the clinical and biological heterogeneity of early-onset CRCs among blacks is ongoing, and critical for understanding global cancer disparities in disease susceptibility and outcomes–which may have implications for tailored early-onset CRC prevention, detection and treatment strategies. Citation Format: Andreana N. Holowatyj, Aishatu Suleiman Maude, Halimatu Sadiya Musa, Ahmed Adamu, Sani Ibrahim, Adamu Abdullahi, Muhammad Manko, Sirajo Mohammed Aminu, Abdullahi Mohammed, John Idoko, Yahaya Ukwenya, John Carpten, Paulette D. Chandler, Heather Hampel, Faruk Mohammed. Distinct patterns of early-onset colorectal cancer among Nigerians and African Americans: An international cohort study [abstract]. In: Proceedings of the AACR Virtual Conference: Thirteenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2020 Oct 2-4. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(12 Suppl):Abstract nr PO-191.