Is ypTNM staging a comparable predictor as pTNM staging for survival in non-metastatic rectal cancer after preoperative chemoradiation therapy?

Background: The pTNM staging system is widely recognized as the most effective prognostic indicator for cancer. The latest update of this staging system introduced a new pathological staging system (ypTNM) for patients receiving neoadjuvant chemoradiotherapy (NACRT). However, whether the prognostic value of the ypTNM staging system for rectal cancer is similar to that of the pTNM staging system remains unclear. This study was conducted to compare the ypTNM and pTNM staging systems in terms of their prognostic value for patients with nonmetastatic rectal cancer undergoing proctectomy. Material and Methods: This study was conducted at a large teaching hospital. Between January 2014 and December 2022, 542 patients with rectal cancer were analyzed (median follow-up period, 60 months; range, 6-105 months). Of them, 258 and 284 were included in the pTNM and ypTNM groups, respectively. Inverse probability of treatment weighting (IPTW) was performed to account for the effects of confounders. Cox proportional-hazards regression was performed for the between-group comparison of overall survival (OS). Results: The crude model revealed that OS was similar between the two groups (p = 0.607). After performing IPTW, we found that patients with the same ypTNM- and pTNM-classified stages had similar overall survival (hazard ratio = 1.15; 95% CI = 0.76-1.73; p = 0.5074). Conclusions: For patients with rectal cancer who have received preoperative NACRT, the prognostic value of ypTNM staging appears to be similar to that of pTNM staging, mostly because of the downstaging effect of neoadjuvant chemoradiotherapy.