Early MRI predictors of disease-free survival in locally advanced rectal cancer from the GRECCAR 4 trial

Background Tailored neoadjuvant treatment of locally advanced rectal cancer (LARC) may improve outcomes. The aim of this study was to determine early MRI prognostic parameters with which to stratify neoadjuvant treatment in patients with LARC. Methods All patients from a prospective, phase II, multicentre randomized study (GRECCAR4; NCT01333709) were included, and underwent rectal MRI before treatment, 4 weeks after induction chemotherapy and after completion of chemoradiotherapy (CRT). Tumour volumetry, MRI tumour regression grade (mrTRG), T and N categories, circumferential resection margin (CRM) status and extramural vascular invasion identified by MRI (mrEMVI) were evaluated. Results A total of 133 randomized patients were analysed. Median follow-up was 41 center dot 4 (95 per cent c.i. 36 center dot 6 to 45 center dot 2) months. Thirty-one patients (23 center dot 3 per cent) developed tumour recurrence. In univariable analysis, mrEMVI at baseline was the only prognostic factor associated with poorer outcome (P = 0 center dot 015). After induction chemotherapy, a larger tumour volume on MRI (P = 0 center dot 019), tumour volume regression of 60 per cent or less (P = 0 center dot 002), involvement of the CRM (P = 0 center dot 037), mrEMVI (P = 0 center dot 026) and a poor mrTRG (P = 0 center dot 023) were associated with poor outcome. After completion of CRT, the absence of complete response on MRI (P = 0 center dot 004), mrEMVI (P = 0 center dot 038) and a poor mrTRG (P = 0 center dot 005) were associated with shorter disease-free survival. A final multivariable model including all significant variables (baseline, after induction, after CRT) revealed that Eastern Cooperative Oncology Group performance status (P = 0 center dot 011), sphincter involvement (P = 0 center dot 009), mrEMVI at baseline (P = 0 center dot 002) and early tumour volume regression of 60 per cent or less after induction (P = 0 center dot 007) were associated with relapse. Conclusion Baseline and early post-treatment MRI parameters are associated with prognosis in LARC. Future preoperative treatment should stratify treatment according to baseline mrEMVI status and early tumour volume regression.