Prospective Determination of Tumor Regression Grade with Magnetic Resonance Imaging in Neoadjuvant Chemotherapy for Rectal Adenocarcinoma

Motivation: The role of MRI in evaluating the tumor response following neoadjuvant chemotherapy (NCT) in rectal cancers remains pending. Goal(s): To investigate the reliability of MRI in assessing the pathological clinical response (pCR) in rectal cancer patients with NCT. Approach: In two consecutive prospective clinical trials (Clinicaltrials.gov NCT03666442 and NCT04922853), tumor responses to NCT were evaluated using MRI-based models. Results: 224 patients were enrolled. MR-TRG, DWI, DWImodMR-TRG mriCR, and rNAR score were all associated with pCR. DWImodMR-TRG achieved the highest area under the curve (AUC) of 0.940, with the highest sensitivity of 0.905 and the highest PPV of 0.976. Impact: MRI-based models were feasible in determining the tumor response in LARC patients following NCT. DWI may improve the predictive performance of MR-TRG. Our findings provide evidence for the determination of tumor response for rectal cancer patients who underwent NCT.