Oncological outcome after MRI-based selection for neoadjuvant chemoradiotherapy in the OCUM Rectal Cancer Trial.

BACKGROUND: It is not clear whether all patients with rectal cancer need chemoradiotherapy. A restrictive use of neoadjuvant chemoradiotherapy (nCRT) based on MRI findings for rectal cancer was investigated in this study. METHODS: This prospective multicentre observational study included patients with stage cT2-4 rectal cancer, with any cN and cM0 status. Carcinomas in the middle and lower third that were 1 mm or less from the mesorectal fascia, all cT4 tumours, and all cT3 tumours of the lower third were classified as high risk, and these patients received nCRT followed by total mesorectal excision (TME). All other carcinomas with a minimum distance of more than 1 mm from the mesorectal fascia and those in the upper third were classified as low risk; these patients underwent TME alone (no nCRT). Patients were followed for at least 3 years. Outcomes were the rates of local recurrence, distant metastasis and survival. RESULTS: Among 545 patients included, 428 were treated according to the study protocol: 254 (59·3 per cent) had TME alone and 174 (40·7 per cent) received nCRT and TME. Median follow-up was 60 months. The 3- and 5-year local recurrence rates were 1·3 and 2·7 per cent respectively, with no differences between the two treatment protocols. Patients with disease requiring nCRT had higher 3- and 5-year rates of distant metastasis (17·3 and 24·9 per cent respectively versus 8·9 and 14·4 per cent in patients who had TME alone; P = 0·005) and worse disease-free survival compared with that in patients who did not need nCRT (3- and 5-year rates 76·7 and 66·7 per cent, versus 84·9 and 76·0 per cent in the TME-alone group; P = 0·016). CONCLUSION: Restriction of nCRT to high-risk patients achieved good results.