The following is a summary of “Prospective Correlation of Magnetic Resonance Tumor Regression Grade With Pathologic Outcomes in Total Neoadjuvant Therapy for Rectal Adenocarcinomatitle,” published in the October 2023 issue of Oncology by Hall, et al.
Total neoadjuvant therapy (TNT) has become the standard treatment for rectal adenocarcinoma. However, current methods for evaluating the magnitude of tumor regression during TNT are often subjective and imprecise. For a study, researchers sought to assess the utility of the Magnetic Resonance Tumor Regression Grade (MR-TRG), a grading system for tumor regression based on magnetic resonance imaging, as well as the addition of diffusion-weighted imaging in predicting pathologic complete response (pCR) in patients undergoing TNT.
The multi-institutional prospective imaging study was conducted within the NRG-GI002 trial. The study analyzed the ability of MRI-based imaging to predict pCR and correlated MR-TRG with the pathologic neoadjuvant response (NAR) score. Serial MRIs from 110 patients were collected and reviewed by three radiologists, independently and collectively. Complete response was assessed for positive predictive value (PPV), negative predictive value (NPV), sensitivity, and specificity with pCR. The association between MR-TRG scores and pCR and NAR was examined.
A total of 121 patients from 71 institutions were included in the study. The majority were White (84%), 28% were female (n = 34) with a median age of 55 (24-78 years). The agreement (kappa scores) between MRI and pathologic stage (T- and N-stage) varied, showing near-perfect agreement for the N-stage but only fair agreement for the T-stage. Calling a mriCR had a kappa score of 0.82 after chemotherapy and 0.56 after TNT, indicating near-perfect and moderate agreement, respectively. MR-TRG scores were associated with pCR and NAR (both P < 0.01), with a PPV for pCR of 40% (95% CI, 26 to 53) and an NPV of 84% (95% CI, 75 to 94).
MRI alone is ineffective for distinguishing pCR in rectal adenocarcinoma patients undergoing TNT. However, the MR-TRG score offers an objectively validated method that correlates with pathologic NAR, providing a means to measure the magnitude of tumor regression during TNT. This could improve the precision and objectivity of assessing treatment response in these patients.