Background: Colorectal cancer (CRC) remains one of the leading causes of cancer-related morbidity and mortality worldwide. Traditionally, CRC has been associated with individuals aged over 50 years, commonly referred to as late-onset colorectal cancer (LO-CRC). In recent years, however, a concerning increase in incidence has been observed among younger adults, a phenomenon known as early-onset colorectal cancer (EO-CRC) EO-CRC occurs in individuals under the age of 50 and information regarding its epidemiology and determinants remains limited.
Objectives: To analyse the sociodemographic, clinical, and histopathological characteristics of colorectal cancer cases diagnosed at Hospital Professor Doutor Fernando Fonseca (HFF), Lisbon, Portugal between January 2003 and December 2023
Methods: An observational study using repeated cross-sectional analyses was conducted. Data were retrospectively collected from clinical records and the National Oncological Registry (RON) at Hospital Professor Doutor Fernando Fonseca (HFF). Proportions and confidence intervals for proportions were calculated using 95% Wilson confidence interval for binomially distributed data. The differences between the rate of EO-CRC and LO-CRC were analyzed using the Mann-Whitney-U-test and the χ2 test. Joinpoint regression was used for trend analysis and logistic regression was used to examine the association between EO-CRC and potential predictors. For statistical analysis we considered a 5% significance level. Statistical analyses were performed using SPSS software (Version 31.0.1.0) with a 5% significance level.Descriptive data analysis was performed for patients and tumor characteristics, and associations were assessed using logistic regression models, with results expressed as odds ratios (ORs) and 95 % confidence intervals (CIs).
Results: A total of 4,889 CRC cases were included in this study, of which 6.4% were EO-CRC. The median age of all patients was 71 years (IQR 62–79), compared with 44 years for EO-CRC, and 72 years for LO-CRC. Males accounted for the majority of cases (59.0%). Tumours were most frequently located in the left colon and rectum (25.7% and 25.0%, respectively), and the predominant histological type was adenocarcinoma (97.7%). Mortality was higher among LO-CRC patients (66.9% vs. 43.3%; p<0,001 in EO-CRC). Joinpoint analysis identified a significant increase in total of CRC cases during the first time segment (2003–2017) (APC = 2.58%; p < 0.001), followed by a significant annual decline in the subsequent period (2018–2023) (APC = –2.29%; p = 0.040), resulting in an overall modest but statistically significant growth trend (AAPC = 0.85%; p = 0.036). Multivariable logistic regression analysis showed that EO-CRC was significantly associated with female sex (OR = 1.35, 95% CI: 1.07–1.71) and with the presence of other tumours (OR = 4.69, 95% CI: 2.06–7.41).
?Conclusions/implications: Colorectal cancer remains a major cause of morbidity, showing an overall modest increase and a reversal temporal trend around 2016. Early-onset colorectal cancer accounts for approximately 6.5% of all CRC cases and although less frequent, is associated with female sex and with rectal and neuroendocrine tumours. These findings highlight the urgent need to review and strengthen both primary prevention measures, such as CRC awareness campaigns, and secondary prevention strategies, including screening programmes, to improve colorectal cancer literacy and reduce the incidence of advanced disease. 

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