A Quantitative Assessment of Discordance Rates Between Preoperative MRI Restaging and Postoperative Pathologic Reports in Patients Undergoing Rectal Resection Following Neoadjuvant Therapy – A Word of Caution Regarding Patient-Selection for watch-and-wait Strategies

Background Accurate restaging after neoadjuvant therapy (NAT) is crucial in the management of rectal cancer, especially in centers that aim to implement organ-preserving watch-and-wait (W&W) strategies for patients achieving complete remission (CR). MRI is the cornerstone of restaging, but its diagnostic accuracy remains debated, with both overstaging and understaging reported. Such discrepancies can lead to unnecessary resections in true complete responders or to potentially detrimental undertreatment in patients with residual disease. Aims This study evaluated the concordance between MRI-based restaging and pathological staging in patients who underwent TME following NAT at our institution. Methods Retrospective analysis of patients with rectal cancer who underwent NAT (chemotherapy, radiotherapy, chemoradiotherapy or immunotherapy) followed by surgical resection between 2018 and 2024 at our institution. Results A total of 113 patients were eligible for analysis. In 51 patients preoperative MRI-based tumor regression grade (ymrTRG) and pathological tumor regression grade (ypTRG) (Dworak) was available. Overall, 31.4% were staged correctly, while 33.3% were overstaged radiologically and 35.3% radiologically understaged. In 38 patients, preoperative ymrT and ypT staging was available. Correct preoperative radiological staging was achieved in 36.8%, while 47.4% were radiologically overstaged and 15.8% radiologically understaged. ymrT0 was reported in 2 patients of which one resulted in ypT0 and the other in ypT1. ypT0 was reported in 6 patients of which only 1 patient had a preoperative ymrT0 staging. Two patients were staged ymrT2, 2 patients ymrT3 and one patient ymrT4. Conclusion MRI restaging after neoadjuvant therapy showed limited accuracy in identifying CR. Both overstaging and understaging were frequent, resulting in clinically relevant consequences. In clinical practice, these findings emphasize the need for a cautious and multimodal approach to restaging. MRI results should always be interpreted in conjunction with endoscopy and digital rectal examination. For centers offering organ-preserving strategies, knowledge of the limited reliability of restaging MRI to detect full remission is crucial for w&w patient selection and early recognition of tumor regrowth.