The role of combining interim and final analysis by using endoscopic and radiologic methods in total neoadjuvant treatment

Background: We aim to compare the relative performance of flexible sigmoidoscopy (FS), rectal magnetic resonance imaging (MRI), and their combinations during interim (i) and final (f) analysis to evaluate concordance with complete response (CR) following total neoadjuvant treatment (TNT) in rectal cancer. Method: Patients who opted TNT and underwent restaging with FS and MRI between 2015 and 2022 were evaluated. Concordance between the assessment methods and CR was analyzed using the weighted-kappa test. Results: A cohort comprising 208 patients revealed CR rate of 42.3 %. When evaluating individual methods, fFS alone demonstrated the most heightened sensitivity (68.2 %) for CR detection, with a moderate level of concordance (kappa 1 / 4 0.46). Only the combinations of iFS-fFS and fFS-fMRI reached a comparable level of concordance to that achievable by fFS alone. Conclusion: Among the available diagnostic tools, the combination of final MRI and FS still appears to offer the highest concordance with CR, with relatively higher sensitivity. Additionally, interim MRI may not add significant clinical value and could be omitted.