Discrepancies between clinical and radiological assessment of complete remission of rectal cancer after neoadjuvant radiochemotherapy

The watch & wait concept in rectal cancer offers a promising non-operative strategy for patients who achieve a complete response following neoadjuvant radiochemotherapy (nRCT). However, accurately diagnosing clinical complete remission (cCR) based on clinical examinations, endoscopy and imaging remains a major challenge. This retrospective study included patients with rectal cancer who received nRCT at the University Hospital Erlangen between May 2022 and July 2024 (radiation: 50.4–54 Gy or 5x5 Gy; chemotherapy: 5-FU and oxaliplatin, partially as part of a total neoadjuvant therapy (TNT) concept). Patients were analyzed based on their clinical, endoscopic, and radiological findings, and classified as having either consistent or discrepant diagnostic results. Particular attention was paid to patients with discrepancies between diagnostic modalities. A total of 78 patients underwent nRCT for rectal cancer during the study period. Six patients were excluded due to a second malignancy, tumor recurrence, or incomplete restaging. 72 patients were included in the final analysis. Of these, 46 patients showed consistent evidence of residual tumor during restaging, leading to surgical resection, with histopathological confirmation of residual tumor in 76% of cases. A clinical and radiological complete remission was observed in 12 of 72 patients (16.7%), four of whom experienced local regrowth. Discrepancies were noted between clinical, endoscopic and radiological findings following nRCT in 14 patients (median age 68 years, range 40–73). Of these patients, 13 had a negative MRI and one had a negative endoscopy, despite differing findings on the other modalities. Diagnosing complete remission after nRCT remains challenging within the context of a watch & wait strategy. Our findings suggest that pelvic MRI may overestimate the response to treatment. This is consistent with published data. Discrepancies between clinical, endoscopic, and radiologic assessments should prompt caution and emphasize the need for individualized decision-making before surgery is omitted.