JCO: MRI may predict rectal cancer survival
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| Axial post-treatment MR image TRG shows a fibrotic low signal scar at 6 o'clock, with high signal intensity submucosal edema; absence of any tumor signal indicates a TRG. Source: Journal of Clinical Oncology. |
"This is the first time that MRI has been shown to predict outcomes for patients with rectal cancer who have completed initial chemoradiation therapy," Gina Brown, MBBS, MD, consultant radiologist and honorary senior lecturer, department of radiology at the Royal Marsden Hospital NHS Trust in Sutton, U.K., said in a statement.
"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."
Brown and colleagues devised a prospective multicenter cohort study as a subgroup analysis of patients enrolled in the MERCURY (Magnetic Resonance Imaging in Rectal Cancer European Equivalence Study) trial. The study enrolled 111 patients with rectal cancer treated by neoadjuvant therapy between February 2002 and October 2003 and completed a five-year follow-up in December 2008.
Researchers used MRI to measure tumor response in terms of tumor regression grade (TRG) and involvement of circumferential resection margin (CRM). Patients were broadly designated either a "good" or "poor" responder to chemoradiation, according to MRI, and researchers compared survival of the two groups.
Brown and colleagues found that 72 percent of good responders to chemotherapy/radiation were alive after five years compared to 27 percent of those who were poor responders. The disease-free survival for those with good responses was 64 percent vs. 31 percent for the poor responders.
In addition, local recurrence rates at five years for those patients for whom there was MRI-predicted CRM involvement was 28 percent compared to 12 percent for patients with predicted cancer-free tumor margins.
“MRI assessment of TRG after preoperative therapy predicts disease-free survival and overall survival, and thus patient prognosis, before definitive surgery. Post-treatment MRI prediction of CRM involvement also gives important prognostic information regarding the risk of local recurrence,” the researchers wrote.
Rectal cancer is commonly found in advanced stages, and as a result, neoadjuvant chemoradiation is frequently given to try to shrink tumors and make them easier to remove. While surgeons attempt to completely remove the cancer in order to minimize the chances of cancer returning, advanced tumors are more difficult to completely remove and more likely to have unseen cancer remaining at the edges of tissue at the surgery site. A positive surgical margin is considered a strong predictor of local recurrence.
Of the 111 patients in the study, 73 percent were expected to have cancer left in the surgical margins prior to initial treatment. After neoadjuvant therapy, 42 percent were predicted to have disease left in the surgery margins.
"The next step is to take these tumor response grades and decide what the best treatment approach could be based on the degree of responses," Brown said.
She noted that future trials investigating neoadjuvant chemotherapy followed by chemoradiotherapy may be able to identify a subgroup of patients that has a good response and for whom chemotherapy alone might be enough, while also identifying those who needed further therapy prior to surgery.
The investigators have begun a trial to study what happens to those individuals who appear to not have any remaining cancer with chemoradiation alone and have deferred surgery. In some cases, this has resulted in long-term deferral with anal sphincter preservation. Other trials may also be designed to use MRI results in regard to treatment efficacy.
As the researchers plan future studies, they emphasized the importance of the results, writing, “This is the first time that a prospective study has demonstrated a correlation between radiologically determined tumor response and long-term outcomes.”