Colorectal cancer in adolescent and young adults: epidemiology in Japan and narrative review.

Background and Objective: Although only a small proportion of colorectal cancer (CRC) cases develop in adolescents and young adults (AYAs), its incidence has increased recently. We aimed to conduct a narrative literature review and summarize the epidemiology, clinicopathological features, genetics, and treatments for AYA-CRCs. Methods: We searched the articles published in the PubMed database until November 30, 2022, with keywords, "((adolescent and young adult) OR AYA) AND ((colorectal cancer) OR (colon cancer) OR (rectal cancer))" and "young-onset AND ((colorectal cancer) OR (colon cancer) OR (rectal cancer))". Key Content and Findings: In Japan, the annual incidence of AYA-CRC was approximately 1,200 in the 1970s, but has increased to 2,000 nowadays. An increased incidence of AYA-CRC has also been reported in other countries. AYA-CRC tends to be a more advanced disease at presentation than CRC in older patients, with more adverse histological features and variability in molecular characteristics. Diagnosis of CRC is often delayed in AYAs because they are not invited to undergo cancer screening. Three to five percent of patients with AYA-CRC have hereditary cancer syndromes such as Lynch syndrome and familial adenomatous polyposis (FAP), and a family history should be obtained. Additionally, providing information on fertility preservation and social systems before starting treatment is important for sustainable treatment and life after cancer treatment. Conclusions: The number of AYA-CRC cases is increasing in Japan. Before initiating treatment for AYA-CRC, we should know that these patients may have a hereditary disease and fertility preservation should be explained. More physicians should be aware of the importance of AYA-CRC.