Diagnostic Accuracy of Post-Neoadjuvant Treatment Restaging Magnetic Resonance Imaging in Rectal Cancer in the Era of Total Neoadjuvant Treatment

Abstract The diagnostic accuracy of a restaging magnetic resonance imaging (MRI) scan after neoadjuvant treatment (NAT), especially total neoadjuvant treatment (TNT), is not well established. We aimed to study the diagnostic accuracy of the restaging MRI after NAT including TNT. This was a retrospective study conducted at a tertiary cancer center of patients undergoing radical surgery after various types of NAT for rectal cancer between 2020 and 2023. The patients were grouped according to the type of NAT received. The findings on the restaging MRI were correlated with the gold standard of the histopathology report of the resected specimen to estimate its diagnostic accuracy overall as well as for the different types of NAT. Among the 131 patients included in this study, 68% received TNT. The restaging MRI showed an overall accuracy of 74.4% for T-stage and 60.1% for N-stage and overestimated the T- and N-stage in 20.6 and 12.2% of patients and underestimated them in 41.2 and 47.3% patients, respectively. MRI had a higher accuracy for T-stage among patients who did not receive TNT compared with those who received it (79.6 vs. 75.2%) but not for N-stage or CRM involvement. The overall sensitivity, specificity, positive predictive value, negative predictive value (NPV), and accuracy of the restaging MRI for CRM involvement were 74.1, 73, 26.8, 95.5, and 74%, respectively. We found a moderate level of accuracy for posttreatment MRI in predicting the pathological stage and a high NPV in determining an involved CRM. Use of TNT reduced the diagnostic accuracy of restaging MRI for T-stage but not for N-stage or predicting CRM involvement. Further studies are required to assess the diagnostic accuracy of posttreatment MRI after different regimens of NAT that are currently recommended in rectal cancer.