Objective To investigate risk factors for metachronous tumor lesions after radical resection of rectal cancer (RC).

Methods Patients who underwent radical resection for RC at The Sixth Affiliated Hospital, Sun Yat-sen University between October 2012 and June 2018 were selected. General patient data, initial colonoscopy findings, and follow-up colonoscopy results before Marth 2025 were collected. Kaplan-Meier analysis was used to compare the cumulative incidence of metachronous tumor lesions between early-onset (EO) and average-onset (AO) RC groups. Univariate and multivariate Cox proportional hazards models were employed to analyze factors associated with developing metachronous tumor lesions after surgery.

Results A total of 757 patients were included, with a follow-up duration of 30 (15, 58) months. Kaplan-Meier analysis demonstrated a significantly lower cumulative risk of metachronous tumor lesions in the EO-RC group compared to the AO-RC group (P＜0.001). Multivariate Cox regression analysis identified EO-RC as a protective factor against metachronous tumor lesions (HR＝0.508, 95%CI: 0.344-0.749). Conversely, PIK3CA mutation (HR＝2.360, 95%CI: 1.340-4.158) and synchronous advanced adenoma (HR＝2.094, 95%CI: 1.401-3.129) were identified as independent risk factors.

Conclusions Patients with EO-RC may not require intensified colonoscopy surveillance postoperatively. However, intensified surveillance strategies should be considered for RC patients harboring PIK3CA mutations or presenting with synchronous advanced adenomas.