Early-Onset Colorectal Cancer: A New Clinical Profile in Patients Treated at a Referral Hospital in Mexico City.

Introduction Early-onset colorectal cancer (EOCRC), defined as colorectal cancer diagnosed before the age of 50, has exhibited a sustained increase in incidence globally. In Mexico, this rising trend presents significant clinical and diagnostic challenges, particularly in younger patients who often lack traditional risk factors. This study aimed to describe and compare the epidemiological, clinical, histopathological, and therapeutic characteristics of EOCRC versus late-onset colorectal cancer (LOCRC) in a referral hospital in Mexico City. Methods We conducted a retrospective observational cohort study at the Hospital General de México, including all patients with histologically confirmed colorectal cancer diagnosed between January 2020 and December 2024. Patients were stratified into two groups based on age at diagnosis: <50 years (EOCRC) and ≥50 years (LOCRC). Variables analyzed included sex, tumor grade, Tumor, Node, Metastasis (TNM) stage, histological subtype, and treatments received (chemotherapy and radiotherapy). Categorical variables were compared using Pearson's Chi-squared or Fisher's exact test, while continuous variables were analyzed using the Wilcoxon rank-sum test. A p-value <0.05 was considered statistically significant, and test statistics were reported accordingly. Results A total of 583 patients were analyzed: 205 (35.2%) in the EOCRC group and 378 (64.8%) in the LOCRC group. The median age at diagnosis was 42.0 years (IQR: 35.0-46.0) for EOCRC and 61.0 years (IQR: 53.0-68.0) for LOCRC (W=0, p<0.001). No significant differences were observed in sex distribution or histological subtype, with adenocarcinoma being the most common in both groups (>90%). Patients with EOCRC were more likely to present with poorly differentiated tumors (24% vs. 15%, χ²=7.85, p=0.020) and were more frequently diagnosed at advanced stages (stage III or IV: 70%). Paradoxically, patients with EOCRC showed a relatively higher proportion of early-stage disease (30% vs. 19%, χ²=23.32, p=0.003) compared to those with LOCRC. Regarding treatment, patients with EOCRC received more adjuvant chemotherapy (69% vs. 59%, χ²=4.20, p=0.040), while those with LOCRC had higher rates of adjuvant radiotherapy (25% vs. 1.5%, χ²=50.88, p<0.001). Conclusion EOCRC represents a distinct clinical and pathological entity compared to LOCRC, characterized by younger age at onset, higher rates of poorly differentiated tumors, and more frequent diagnosis at advanced stages. These findings highlight the need for increased clinical vigilance, age-adjusted screening strategies, and further molecular studies to better understand the underlying biology of EOCRC in younger populations.