Perineural Invasion as a High-Risk Feature Is Not a Predictive Biomarker for Postoperative Adjuvant Radiotherapy in Stage II Low Rectal Cancer: A Retrospective Analysis of a Real-World Cohort

Background Perineural invasion (PNI), though reported with varying incidence in rectal cancer, is a recognized marker of adverse prognosis. While postoperative adjuvant radiotherapy is a cornerstone of multidisciplinary management of locally advanced rectal cancer, its benefit for stage II rectal cancer (RC) with perineural invasion remains debated. Methods A retrospective analysis was conducted on 211 patients with stage II RC who underwent radical surgery at our center between 2016 and 2019. Cox regression analysis was used to determine prognostic factors, and Kaplan-Meier (KM) curves and log-rank tests were used to analyze differences in overall survival (OS) and disease-free survival (DFS) among different groups. Results Among the 211 stage II RC, 47 (22.3%) were identified as PNI-positive (PNI+). PNI + was significantly correlated with elevated preoperative carcinoembryonic antigen (CEA) levels and higher T stage. Multivariate Cox regression identified PNI is an independent prognostic factor for worse DFS and OS specifically in low rectal cancer, but not in high rectal cancer. RC patients with PNI- demonstrated superior 5-year OS and DFS compared to PNI+. Notably, Postoperative adjuvant radiotherapy did not improve the prognosis of patients with stage II low PNI + RC. Conclusion PNI is an independent prognostic factor for DFS and OS of stage II Low RC, but PNI + RC cannot derive benefit from postoperative adjuvant radiotherapy.