Long-term Follow-up Features on Rectal MRI During a Wait-and-See Approach After a Clinical Complete Response in Patients With Rectal Cancer Treated With Chemoradiotherapy

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The "wait-and-see" policy instead of standard surgery for patients with rectal cancer who undergo a complete tumor regression after chemoradiation treatment is highly controversial. It is not clear yet how patients should be monitored once they are managed nonoperatively and whether follow-up by MRI has any potential role. This study aimed to describe the rectal wall MRI morphology during short-term and long-term follow-up in patients with a clinical complete tumor response undergoing a wait-and-see policy without surgical treatment. As part of an observational study in our center, a cohort of 19 carefully selected patients with a clinical complete response after chemoradiation was managed with a wait-and-see policy and followed regularly (every 3-6 mo) by clinical examination, endoscopy with biopsies, and a rectal MRI. The MR morphology of the tumor bed was studied on the consecutive MRI examinations. The primary outcome measured was the morphology of the tumor bed on the consecutive MRI examinations performed during short-term (≤6 mo) and long-term (>6 mo) follow-up. Patients with a complete tumor response after chemoradiation presented with either a normalized rectal wall (26%) or fibrosis (74%). In the latter group, 3 patterns of fibrosis were observed (full-thickness, minimal, or spicular fibrosis). The morphology patterns of a normalized rectal wall or fibrosis remained consistent during long-term follow-up in 18 of 19 patients. One patient developed a small, endoluminal recurrence, which was salvaged with transanal endoscopic microsurgery. In 26% of patients, an edematous wall thickening was observed in the first months after chemoradiation, which gradually decreased during long-term follow-up. Median follow-up was 22 months (range, 12-60). This was a small observational study, and had no histological validation. Four MR patterns of a persistent complete response of rectal cancer after chemoradiation were identified. These MR features can serve as a reference for the follow-up in a wait-and-see policy.