Combination Assessment of Clinical Complete Response of Patients With Rectal Cancer Following Chemoradiotherapy With Endoscopy and Magnetic Resonance Imaging

Purpose: The response to neoadjuvant chemoradiotherapy (CRT) for rectal cancer can be assessed using digital rectal examination, endoscopy and magnetic resonance imaging (MRI). Precise assessment of clinical complete response (CR) after CRT is essential when deciding between optimizing surgery or organ-preserving treatment. The objectives of this study were to correlate the CR finding in endoscopy and MRI with pathologic CR and to determine the appropriate approach for combining endoscopy and MRI to predict the pathologic CR in patients with rectal cancer after neoadjuvant CRT. Methods: This retrospective cohort study included 102 patients with rectal cancer who underwent endoscopy and MRI at 2-4 weeks after CRT. We assigned a confidence level (1-4) for the endoscopic and MRI assessments. Accuracy, sensitivity, and specificity were analyzed based on the endoscopy, MRI, and combination method findings. Diagnostic modalities were compared using the likelihood ratios. Results: Of 102 patients, 17 (16.7%) had a CR. The accuracy, sensitivity, and specificity for the prediction CR of endoscopy with biopsy were 85.3%, 52.9%, and 91.8%, while those of MRI were 91.2%, 70.6%, and 95.3%, and those of combined endoscopy and MRI were 89.2%, 52.9%, and 96.5%, respectively. No significant differences were noted in the sensitivity and specificity of any each modality. The prediction rate for CR of the combination method was 92.6% after the posttest probability test. Conclusion: Our study demonstrated that combining the interpretation of endoscopy with biopsy and MRI could provide a good prediction rate for CR in patients with rectal cancer after CRT.