Contemporary snapshot of tumor regression grade (TRG) distribution in locally advanced rectal cancer: a cross sectional multicentric experience

Pre-operative chemoradiotherapy (CRT) followed by surgical resection is still the standard treatment for locally advancedlow rectal cancer. Nowadays new strategies are emerging to treat patients with a complete response to pre-operative treatment,rendering the optimal management still controversial and under debate. The primary aim of this study was to obtaina snapshot of tumor regression grade (TRG) distribution after standard CRT. Second, we aimed to identify a correlationbetween clinical tumor stage (cT) and TRG, and to define the accuracy of magnetic resonance imaging (MRI) in the restagingsetting. Between January 2017 and June 2019, a cross sectional multicentric study was performed in 22 referral centers ofcolon-rectal surgery including all patients with cT3-4Nx/cTxN1-2 rectal cancer who underwent pre-operative CRT. Shapiro–Wilk test was used for continuous data. Categorical variables were compared with Chi-squared test or Fisher’s exact test,where appropriate. Accuracy of restaging MRI in the identification of pathologic complete response (pCR) was determinedevaluating the correspondence with the histopathological examination of surgical specimens.In the present study, 689 patients were enrolled. Complete tumor regression rate was 16.9%. The “watch and wait” strategywas applied in 4.3% of TRG4 patients. A clinical correlation between more advanced tumors and moderate to absent tumorregression was found (p = 0.03). Post-neoadjuvant MRI had low sensibility (55%) and high specificity (83%) with accuracyof 82.8% in identifying TRG4 and pCR.Our data provided a contemporary description of the effects of pre-operative CRT on a large pool of locally advanced lowrectal cancer patients treated in different colon-rectal surgical centers.