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MRI May Predict Survival After Neoadjuvant Therapy for Rectal Cancer

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MRI of rectal cancer may be used to predict outcomes, new research shows. (Image by permission of high-resolution magnetic resonance imaging (MRI) researchers have shown for the first time that MR imaging can be used to assess neoadjuvant treatment response before surgery for rectal cancer. The researchers concluded that MRI may also be used to predict overall and disease-free survival in these patients.

The researchers led by Dr. Gina Brown, honorary senior lecturer in the Department of Radiology at the Royal Marsden Hospital in Sutton, UK, analyzed the results of a subgroup of the MERCURY trial to measure tumor shrinkage in 111 patients treated with chemotherapy, radiation or both before surgery. Brown told The Hub by e-mail that the difference in this study and previous research was that the radiologists in this study paid careful attention to circumferential resection margins (CRM) and fibrosis following treatment.

“There had been a number of papers stating how unreliable imaging was for reassessment after chemoradiotherapy, which discouraged clinical teams using the information to plan surgery or further treatment,” Brown said. “These papers had not considered reevaluation of the CRM nor had they looked at the degree of treatment induced fibrosis as an assessment of tumor response and shrinkage.”

In their study appearing in the September issue of the Journal of Clinical Oncology, the British researchers combined high resolution MRI with uniform criteria for reading the images and included additional training.

“In the current publication, a high resolution MRI technique was used and reporting criteria were rigidly standardized through workshops,” Brown said. “I still see poor quality scans being done for rectal cancer staging – so specialization and development of colorectal multidisciplinary teams with a consistent dedicated team of radiologists is also essential.”

In the Magnetic Resonance Imaging in Rectal Cancer European Equivalence Study (MERCURY) begun in 2002, patients were enrolled at 11 colorectal specialty units in five European countries. The objective was to evaluate diagnostic accuracy of MRI staging of rectal cancer.

This study was a subgroup analysis of 58 patients who underwent neoadjuvant radiotherapy and 53 who received long-course chemoradiotherapy with fluoropyrimidine prior to surgery for locally advanced rectal cancer.

Tumor response was categorized based on tumor regression grade (TRG) and circumferential resection margins into good and poor responders to enable binary comparison by multivariate analysis. MRI-predicted involvement of CRM and pathologic CRM involved were defined as poor, whereas clear pathologic CRM and magnetic resonance CRM were classified as good.

Of 111 patients undergoing preoperative therapy, 92 also underwent post-treatment MRI before surgery. Sixty-six (72 percent) of 92 pre-and post-treatment scans were available for central review of mrTRG.

Of the 111 patients in the study, 73 percent (81 patients) were expected to have cancer left in the surgical margins prior to initial treatment. After neoadjuvant therapy, only 42 percent (47 patients) were predicted to have disease left in the surgery margins, meaning this group was still at risk for recurrence prior to surgery.

As of December 2008, surviving patients had been observed for a median of 50 months. A total of 54 patients died; 40 died as a result of cancer-related causes, five died as a result of non-cancer deaths, four died as a result of peri- or post-operative causes, and three patients died as a result of unknown causes. Fifty patients had disease progression; 42 patients experienced recurrence with metastatic disease, and eight experienced relapse with local recurrence only.

Overall survival at five years for patients with poor mrTRG was 27 percent compared with 72 percent for patients with good mrTRG. Disease-free-survival at five years for patients with poor mrTRG was 31 percent compared with 64 percent for patients with good mrTRG.

"This is the first time that MRI has been shown to predict outcomes for patients with rectal cancer who have completed initial chemoradiation therapy," Brown said. "MRI staging and reassessment of rectal cancers before and after chemoradiotherapy are not routinely done for all patients. We've shown that using MRI this way can help change the course of patient care, perhaps enabling physicians to choose a more effective chemotherapy drug or even in some cases ultimately avoid surgery."

By Michael O’Leary, contributing writer, Health Imaging Hub

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