[Comparative study of clinical characteristics and prognosis between early- and late-onset rectal cancer]

Objective: To investigate the differences in clinical characteristics and prognosis between early- and late-onset rectal cancer (EORC and LORC, respectively), and to analyze the adverse factors affecting outcomes in EORC patients. Methods: This retrospective cohort and propensity score matching (PSM) study examined 904 rectal cancer patients who underwent radical resection at Peking University Shougang Hospital between 2017 and 2022. Prior to comparison, patients in the EORC group (<50 years old) and LORC group (≥50 years old) were matched at a 1:2 ratio to control for the following confounders: sex; neoadjuvant therapy; T, N, and M stage; and adjuvant treatment. Cox regression was used to identify independent risk factors for poor overall and progression-free survival (OS and PFS, respectively). Restricted cubic splines were used to analyze the association between age and clinical outcome. Results: A total of 199 EORC and 705 LORC patients were included for analysis. Prior to PSM, the proportions of patients with stage T4 [27.6%(55/199) vs.12.9%(91/705),χ²=30.12,P<0.001] and M1 disease [24.6%(49/199) vs. 15.7% (111/705),χ²=8.40,P=0.004], and the proportions of patients who received neoadjuvant [79.9% (159/199) vs. 62.3%(439/705), χ²=21.54, P<0.001] and adjuvant therapy [62.8%(125/199) vs. 50.8% (358/705), χ²=9.03, P=0.003] were significantly higher in the EORC group. Mean OS (57.8 vs. 51.9 months; P=0.011) and PFS (53.6 vs. 44.5 months; P=0.001) were also significantly longer in the LORC group. However, after PSM, the intergroup differences in OS and PFS were not significant (P=0.450 and 0.180, respectively). Multivariate Cox regression in the EORC cohort identified carcinoembryonic antigen concentration ≥5 μg/L [hazard ratio (HR), 3.79; 95% confidence interval (CI), 1.34-10.69; P=0.012] and presence of perineural invasion (HR, 7.27; 95%CI, 1.77-29.88; P=0.006) as independent risk factors for overall mortality; the only independent risk factor for cancer progression was carcinoembryonic antigen concentration ≥5 μg/L (HR, 2.56; 95%CI, 1.06-6.17; P=0.037). Restricted cubic spline analysis showed a U-shaped relationship between age and clinical outcome. After PSM, OS and PFS did not show a significant association with age in the < 60 years old group. Conclusion: Compared with LORC, EORC is more likely to be diagnosed at a later stage and has a worse outcome. Early diagnosis and timely treatment improve outcome in EORC patients.