Predictive Value of Endoscopic Features for a Complete Response After Chemoradiotherapy for Rectal Cancer

Watch-and-wait approach in rectal cancer relies on the identification of a clinical complete response (CR) after neoadjuvant (chemo)radiotherapy. This is mainly performed by rectal examination, magnetic resonance imaging, and endoscopy. Endoscopy has been less well studied, and the objective of the study is to assess the diagnostic value of endoscopy and the predictive value of endoscopic features for the identification of CR.

A total of 161 patients with primary rectal cancer undergoing flexible sigmoidoscopy for response assessment after neoadjuvant (chemo)radiotherapy between January 2012 and December 2015 at a single institution were evaluated retrospectively. Three independent readers scored endoscopic features and a confidence level score for a CR. Diagnostic performance of endoscopy and positive predictive value (PPV) of endoscopic features for a CR were calculated. If available, biopsy results were revealed to the reader and a change in confidence level was noted. Reference standard was histology after surgery, or long-term outcome in a watch-and-wait policy.

Median time to endoscopy was 9 (interquartile range 8-12) weeks. Area under the receiver operator characteristic curve, sensitivity, specificity, PPV, and negative predictive value for a CR were 0.80 to 0.84, 72% to 94%, 61% to 85%, 63% to 78% and 80% to 89%, respectively. A flat scar was the most predictive feature of a CR (PPV 70%-80%). The PPV of small flat ulcers and large flat ulcers were 40% to 50% and 29% to 33%, respectively. The addition of biopsy results led to a significant change in confidence level score in 4% to 13% of patients.

More than 70% of the patients with a luminal CR after neoadjuvant treatment for rectal cancer can be identified by endoscopy at ±9 weeks. Together with findings on digital rectal examination (DRE) and magnetic resonance imaging, specific endoscopic features can be used to select patients for an extended observation period to select for organ preservation.