Clinicopathologic and Racial/Ethnic Differences of Colorectal Cancer Among Adolescents and Young Adults.

OBJECTIVES: Despite overall reductions in colorectal cancer burden, incidence rates continue to rise among younger patients, and causes remain unknown. We examined differences in clinicopathologic and racial/ethnic characteristics within the adolescent and young adult (AYA) population diagnosed with colorectal cancer in the United States. METHODS: Using the National Cancer Institute's Surveillance, Epidemiology, and End Results program data, we identified individuals diagnosed with first primary colorectal cancer between ages 15 and 39 years from 2010 to 2015. Adjusted multivariable logistic regression models were used to quantify clinicopathologic and racial/ethnic differences across age at onset subgroups (15-19, 20-24, 25-29, 30-34, and 35-39 years). RESULTS: We identified 5,350 AYA patients diagnosed with colorectal cancer. Of note, 28.6% of AYA cases were diagnosed with right-sided tumors (cecumto transverse colon). The proportion of right-sided colorectal cancers differed significantly by age group at diagnosis (38.3% vs 27.3% of AYAs aged 15-19 vs 35-39 years, respectively; P trend = 0.01). Proportions of cases with mucinous adenocarcinoma and signet ring cell carcinoma histopathologic subtypes significantly increased with younger age at onset (P trends = 0.01 and 0.03, respectively). Differences in clinical stage were observed across AYA age groups, with stage II disease increasing with younger age (P trend = 0.01). The proportion of Hispanic AYAs was higher within younger patients, accounting for 21.0% of the AYA population aged 35-39 years up to 28.3% of 15-19-year-old individuals (P trend = 0.003). DISCUSSION: Within the AYA population, colorectal cancers differ by clinicopathologic and racial/ethnic characteristics. Further investigation of the clinical and biologic diversity of colorectal cancers that partially underlie age- and race-related differences in cancer susceptibility and outcomes is warranted.