Correlation of Tumor Response Between Flexible Sigmoidoscopy and Magnetic Resonance Imaging in Patients Undergoing Neoadjuvant Therapy for Locally Advanced Rectal Cancer: A Retrospective Review.

Background: The National Accreditation Program for Rectal Cancer recommends a pelvic MRI to assess the response to neoadjuvant therapy for advanced rectal cancers. However, there is no single restaging modality that can identify all patients with complete tumor response. At our institution, we perform both a pelvic MRI and a flexible sigmoidoscopy (FS) after neoadjuvant therapy prior to surgical resection.

Objective: to elucidate the correlation of tumor response between FS and MRI in patients undergoing neoadjuvant therapy for locally advanced rectal cancer.

Design: Single institution from 2010 to 2019. Retrospective cohort study comparing local tumor response on FS to MRI utilizing final pathology as the gold standard for comparison.

Patients: Patients with confirmed locally advanced rectal adenocarcinoma (stage II or III) who underwent neoadjuvant therapy prior to surgical intervention and underwent flexible endoscopy and a standardized rectal cancer protocol MRI to evaluate tumor response.

Results: A total of 48 patients were evaluated. Seven (14%) patients had a complete pathological response. MRI adequately reported 1 (14%), while FS found 4 (57.14%) out of the 7 complete responders. Nevertheless, this did not reach statistical significance ( = .06). On logistic regression analysis, flexible sigmoidoscopy had a 5.5 higher likelihood to report an accurate complete response (OR 5.5, 95% CI: 1.02-29.64; = .047).

Conclusions: Flexible sigmoidoscopy should be used in conjunction with MRI in the work up of patients who have received neoadjuvant therapy for advanced rectal cancer prior to surgical resection.