Accuracy of Flexible Sigmoidoscopy and MRI in Restaging Rectal Cancer after Neoadjuvant Therapy: A Secondary Analysis of the OPRA Randomized Clinical Trial.

Abstract

To measure the accuracy of flexible sigmoidoscopy (FS) and MRI in identifying a true response (TR) to total neoadjuvant therapy (TNT) in patients with locally advanced rectal cancer. Tumor response on restaging FS and MRI determines patient eligibility for watch-and-wait (WW). Prospective studies have not yet evaluated the accuracy of these testing modalities. This was a secondary analysis of the OPRA trial. Patients underwent restaging assessment with FS and MRI 8±4 weeks after completing TNT. Those with a clinical complete (cCR) or near-complete (nCR) response were recommended for WW. Patients with an incomplete response were recommended for total mesorectal excision. A TR, defined as a sustained cCR for ≥2 years on WW or a pathologic complete response on surgical specimen, was the reference standard for the diagnostic performance analysis. Three hundred and four patients completed TNT; 265 (82%) had sufficient follow-up for inclusion in the diagnostic performance analysis. Fifty-two percent had a TR. Accuracy, sensitivity and specificity were 60%, 95% and 23% for MRI and 65%, 96% and 33% for FS. Combining FS and MRI improved accuracy to 67%. The combined modalities reliably predicted 5-year TME-free survival (log-rank P<0.001), with patients whose tumor response was classified as nCR by both assessments most likely to experience local regrowth. Endoscopic and radiologic assessment of rectal tumor response to neoadjuvant therapy is accurate in two-thirds of patients. FS is more likely than MRI to detect a TR and should take precedence when exams are discordant.