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

Methods A retrospective study was conducted on 757 RC patients who underwent RC radical surgery at the Sixth Affiliated Hospital, Sun Yat-sen University from October 2012 to June 2018. The patients were divided into early-onset RC group (EO-RC group, ＜50 years old, n=228) and average-onset RC group (AO-RC group, ≥ 50 years old, n=529) based on their age of diagnosis, and were followed up until March 2025. General information, initial colonoscopy, follow-up colonoscopy, and other relevant clinical information were collected from all patients. The risk of developing metachronous tumor lesions was compared between two groups using Kaplan Meier (K-M) risk function; univariate and multivariate Cox proportional hazards models were used to analyze the influencing factors of metachronous tumor lesions after RC radical surgery.

Results The median follow-up time was 30 (15, 58) months. The K-M risk function showed that the risk of developing metachronous tumor lesions in the EO-RC group was significantly lower than that in the AO-RC group (P＜0.001). The results of the multivariate Cox proportional hazards model showed that the risk of metachronous tumor lesions after RC surgery in the EO-RC group was 50.8% of that in the AO-RC group (P＜0.001); PIK3CA mutation and synchronous advanced adenoma were independent risk factors for metachronous tumor lesions after RC surgery (HR=2.360, 2.094; P=0.003, P＜0.001).

Conclusions RC patients with advanced age, PIK3CA mutations, and synchronous advanced adenomas are prone to developing metachronous tumor lesions after surgery. 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.