Magnetic Resonance Imaging After Total Neoadjuvant Therapy in Rectal Cancer: Treatment-Oriented Response Assessment and Reporting for Watch-and-Wait Management.

Total neoadjuvant therapy (TNT) is increasingly recognized as a standard treatment option for locally advanced rectal cancer. By increasing rates of clinical complete response (cCR) and thereby expanding opportunities for nonoperative management, TNT has elevated the role of magnetic resonance imaging (MRI) in assessment of rectal cancer treatment response. Restaging MRI is shifting away from reliance on tumor regression grading systems, which have demonstrated limited correlation with pathologic findings, toward more clinically relevant assessments integrated with flexible endoscopy. The identification of cCR now incorporates diffusion-weighted imaging to improve sensitivity for detecting residual tumors and specificity for confirming cCR, thereby enabling safer selection of patients eligible for organ preservation. Growing acceptance that small foci of residual tumor, consistent with a near-complete response, can be safely managed with short-interval surveillance has further broadened eligibility for nonoperative management, reinforcing the central role of MRI in contemporary rectal cancer care.