Predictors of pathologic complete response in patients with residual flat mucosal lesions after neoadjuvant chemoradiotherapy for locally advanced rectal cancer.

Objective: The accurate prediction of tumor response to neoadjuvant chemoradiotherapy (nCRT) remains challenging. Few studies have investigated pathologic complete response (ypCR) prediction in patients with residual flat mucosal lesions after treatment. This study aimed to identify variables for predicting ypCR in patients with residual flat mucosal lesions after nCRT for locally advanced rectal cancer (LARC). Methods: Data of patients with residual flat mucosal lesions after nCRT who underwent radical resection between 2009 and 2015 were retrospectively collected from the LARC database at Peking University Cancer Hospital. Univariate and multivariate analyses of the association between clinicopathological factors and ypCR were performed, and a nomogram was constructed by incorporating the significant predictors. Results: Of the 246 patients with residual flat mucosal lesions included in the final analysis, 56 (22.8%) had ypCR. Univariate and multivariate analyses showed that pretreatment cT stage (pre-cT) ≤T2 (P=0.016), magnetic resonance tumor regression grade (MR-TRG) 1-3 (P=0.001) and residual mucosal lesion depth =0 mm (P<0.001) were associated with a higher rate of ypCR. A nomogram was developed with a concordance index (C-index) of 0.759 and the calibration curve showed that the nomogram model had good predictive consistency. The follow-up time ranged from 3.0 to 113.3 months, with a median follow-up time of 63.77 months. The multivariate Cox regression model showed that the four variables in the nomogram model were not risk factors for disease-free survival (DFS) or overall survival (OS). Conclusions: Completely flat mucosa, early cT stage and good MR-TRG were predictive factors for ypCR instead of DFS or OS in patients with LARC with residual flat mucosal lesions after nCRT. Endoscopic mucosal re-evaluation before surgery is important, as it may contribute to decision-making and facilitate nonoperative management or organ preservation.