MR Tumor Regression Grade Can Help Oncologists Guide Treatment for Patients with Rectal Cancer

TumorTotal neoadjuvant therapy (TNT) is a newly-established standard treatment for rectal adenocarcinoma, a type of cancer that starts in the glandular cells of the rectum. However, the current methods to characterize rectal tumor regression during TNT are subjective and imprecise, making it difficult for oncologists to understand whether the treatment is achieving the desired outcomes. New MCW research, published in the Journal of Clinical Oncology, revealed that when used alone, magnetic resonance (MR)-based imaging—the standard of care for grading tumors in those with rectal adenocarcinoma—is an insufficient tool for measuring pathologic complete response (pCR) in patients undergoing TNT.

“Results showed the positive predictive value associated with MR tumor regression grade (MR-TRG) alone in describing pCR was approximately 40%, no better than a coin flip,” said first author William A. Hall, MD, Professor, Radiation Oncology. “This knowledge is essential for oncologists to consider when managing patients with rectal cancer treated with TNT.”

“The insights generated from this study are critical in a TNT era where exquisite focus is being placed on selecting patients for nonoperative management. Physical examination and endoscopy are clearly indispensable tools for this task,” Dr. Hall added.

Current studies demonstrate that 30%-50% of patients can achieve nonoperative management when undergoing TNT, creating a considerable need for accurate clinical assessment of tumor regression. Investigators took a closer look at MRI’s reliability by conducting a prospective imaging sub-study within the phase 2 NRG-GI002 trial that tests a novel radiosensitizer in patients with rectal adenocarcinoma undergoing TNT. While results showed that MR-TRG is a poor tool to predict pCR to TNT, the team learned it can be used as a strategy to objectively describe rectal tumor regression during the treatment.

“This is the first study to present such a characterization of MRIs across a prospective multi-institutional patient cohort being managed with TNT in a uniform manner with consistent treatment, imaging, and pathology acquisition time points,” Dr. Hall noted.

Several follow-up studies have been published using the MR-TRG, but adoption of the scoring system within the oncologic community has not taken place. Dr. Hall explained this is likely due to their retrospective and single-institutional cohort data, along with the absence of validation in a TNT population. Findings presented in this study may open the door for MR-TRG to be used as a succinct clinical scoring system in adaptive prospective TNT clinical trials.

“Characterizing tumor regression is a multifaceted process that integrates clinical, radiological, pathological, and molecular data to comprehensively assess the response of a tumor to treatment. It is a crucial step in tailoring cancer therapies to individual patients and improving treatment outcomes,” said Dr. Hall.