Magnetic resonance imaging (MRI) can be used after neoadjuvant therapy for rectal cancer to predict survival outcomes for good and poor responders and offer patients additional treatment options before definitive surgery, according to a study conducted at 11 specialist colorectal cancer units in five European countries. “This is the first time that a prospective study has demonstrated a correlation between radiologically determined tumor response and long-term outcomes,” the investigators reported in the Journal of Clinical Oncology.
In this prospective cohort study, 111 patients with rectal cancer treated by neoadjuvant therapy were assessed for response by MRI and pathology staging by tumor, node, and circumferential resection margin status. Tumor regression grade was also assessed by MRI. The study is a planned subgroup analysis of patients undergoing neoadjuvant therapy and total mesorectal excision surgery in the MERCURY (Magnetic Resonance Imaging in Rectal Cancer European Equivalence Study) trial.
Overall survival at 5 years for patients with poor tumor regression grade as assessed by MRI was 27% vs 72% for patients with good tumor regression grade on MRI (P= .001), while disease-free survival was 31% vs 64% (P = .007). “Preoperative MRI-predicted [circumferential resection margin] independently predicted local recurrence,” the researchers reported. Local recurrence rates at 5 years were 28% for patients with predicted circumferential resection margin involvment on MRI vs 12% for patients with a predicted clear margin on MRI (P = .013).
Postoperative histopathology assessment of circumferential resection margin was significant on multivariate analysis for overall survival, disease-free survival, and local recurrence. Five-year survival for patients with poor post-treatment pathologic T stage was 39% vs 76% for patients with good pathologic T stage (P= .001). “Pathology node status did not predict outcomes,” the investigators noted.
MRI assessment of tumor regression grade after preoperative therapy predicts disease-free and overall survival, and thus patient prognosis, before definitive surgery, the authors concluded. “Post-treatment MRI prediction of [circumferential resection margin] involvement also gives important prognostic information regarding the risk of [local recurrence].” ■
Patel UB, et al: J Clin Oncol 29:3753-3760, 2011.