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Background: Colorectal cancer (CRC) incidence and mortality in those aged 50 years and above have decreased over the last 2 decades. However, there is a rising incidence in CRC among individuals under 50 years of age, termed early-onset colorectal cancer (EOCRC). EOCRC patients are more advanced stage at diagnosis and may suffer more psychosocial, emotional and financial distress., Objective: Our study examines the epidemiological shifts of CRC in Singapore, a multiethnic country., Methods: CRCs diagnosed at age 20 and above from 1968 to 2019 were identified from the Singapore Cancer Registry. Patient characteristics included gender, ethnicity and age of diagnosis of CRC. Population information was obtained from the Department of Statistics Singapore. Age specific incidence rates (ASR) and age standardized incidence rates (ASIR) were calculated. The cohort was divided into 3 age groups: 20 - 49, 50 - 64 and ≥65 years. Temporal trends of incidence rates were modelled with Joinpoint Regression. Birth cohort models were fitted using the National Cancer Institute (NCI) age-period-cohort analysis tool. Cancer-specific survival analysis was performed with Cox proportional hazards model., Results: 53044 CRCs were included, and 6183 (11.7%) adults aged 20 to 49 years were diagnosed with EOCRC. ASR of EOCRC rose from 5 in 1968 to 9 per 100,000 in 1996 at 2.1% annually and rose to 10 per 100,000 in 2019 at 0.64% annually. The ASR for CRC among adults 50 to 64 years rose at 3% annually from 1968 to 1987 and plateaued from 1987 while the ASR for adults aged 65 and above rose at 4.1% from 1968 to 1989 and 1.3% annually from 1989 to 2003 but decreased from 2003 onwards at 1% annually. There is a continued rise in the ASR of EOCRC among males (APC: 1.5%) compared to females (APC: 0.41%) and a significant increase in APC for early-onset rectal cancer at 1.5% yearly. Compared to the 1950 - 1954 birth reference cohort, the 1970 - 1984 birth cohort had a significantly higher incidence rate ratio (IRR) of 1.17 - 1.36 for rectal cancer while there was no significant change for colon cancer in later cohorts. There were differences in CRC trends across the 3 ethnic groups. Malays had a rapid and persistent rise in ASR of CRC across all age groups (APC: 2- 3%) while amongst young Chinese, only the ASR of rectal cancer is increasing (APC: 1.5%). EOCRC patients had better survival compared to patients diagnosed at 65 years and above (HR 0.73, 95% CI 0.67 - 0.79, P <0.001) after adjusting for covariates., Conclusions: The rise in incidence of rectal cancer among young adults especially among Chinese and Malays in Singapore highlights the need for further research to diagnose CRC earlier and reduce cancer-related morbidity and mortality.