LAUSR

Abstract Background Overall colorectal cancer (CRC) incidence and mortality are declining due to cancer screening in older patients population, however, the incidence of CRC is increasing in younger adults ( Methods Medical record of patients who were diagnosed adenocarcinoma of colorectal cancer at Siriraj Hospital between 2007 and 2018 were retrospectively reviewed. The patients were classified into 2 groups: AYA-onset CRC (age 15-39 years) and adult-onset CRC (age >50 years). Associations between sporadic microsatellite stable (MSS) AYA- /adult-onset CRC and clinicaopathological features and outcome were evaluated. Results A total 202 patients were diagnosed with AYA-onset CRC with no known history of familial CRC syndromes, 116 had data on mismatch repair status; 94 confirmed MSS CRC. AYA-onset CRC patients were commonly found with left-sided rather than right-sided tumors (77.7% vs 21.8%) and late stage of disease (72.7% in stage III-IV vs 24.7% in stage I-II). Compared with adult-onset CRC (195 patients), AYA-onset MSS CRC had more patients with female gender (p = 0.042), signet ring cell/mucinous histology (P = 0.039), and perineuralinvasion (P = 0.004). On univariate analysis, male gender and mucinous/signet ring cell histology had significantly worse OS (P = 0.003 and P = 0.016, respectively) and remained significant in multivariate analysis. There was no differences in terms of DFS or OS in both age groups. Conclusions Sporadic MSS AYA-onset CRC in Thai patients was associated with female gender and aggressive pathological characteristics. However, there was no difference in survival outcome between AYA-onset and adult-onset groups. Legal entity responsible for the study The authors. Funding Siriraj Research Fund. Disclosure All authors have declared no conflicts of interest.