Endoscopic Predictors of Residual Tumor after Total Neoadjuvant Therapy: A Post Hoc Analysis from the Organ Preservation in Rectal Adenocarcinoma Trial

BACKGROUND: Restaging endoscopy plays a critical role in selecting patients with locally advanced rectal cancer who respond to neoadjuvant therapy for nonoperative management. OBJECTIVE: This study evaluated the restaging endoscopic features that best predict the presence of residual tumor in the bowel wall. DESIGN: This was a post hoc analysis of a prospective randomized trial. SETTINGS: The Organ Preservation in Rectal Adenocarcinoma Trial randomly assigned patients across 18 institutions with stage II/III rectal adenocarcinoma to receive either induction or consolidation total neoadjuvant therapy. Surgeons completed a restaging tumor assessment form, which stratified patients across 3 tiers of clinical response. PATIENTS: Patients enrolled in the Organ Preservation in Rectal Adenocarcinoma Trial with a completed tumor assessment form were included. MAIN OUTCOME MEASURES: The main outcome was residual tumor, which was defined as either an incomplete clinical response or local tumor regrowth within 2 years of restaging. Independent predictors of residual tumor were identified using backward-selected multivariable logistic regression analysis. Subgroup analyses for complete and near complete clinical responders were performed. RESULTS: Surgeons completed restaging forms for 263 patients at a median of 7.7 weeks after neoadjuvant therapy; 128 patients (48.7%) had a residual tumor. On multivariable regression analysis, several characteristics of a near complete response, including ulcer (OR 6.66; 95% CI, 2.54-19.9), irregular mucosa (OR 3.66; 95% CI, 1.61-8.68), and nodularity (OR 2.96; 95% CI, 1.36-6.58), remained independent predictors of residual tumor. A flat scar was associated with lower odds of harboring residual disease (OR 0.32; 95% CI, 0.11-0.93) for patients categorized as clinical complete responders. LIMITATIONS: Limitations include analysis of endoscopic features at a single time point and ambiguities in tumor assessment form response criteria. CONCLUSIONS: Patients with ulcer, nodularity, or irregular mucosa, on restaging endoscopy have higher odds of residual tumor. Recognizing negative prognostic implications of these features will help surgeons better select candidates for nonoperative management and suggests that patients with high-risk characteristics would benefit from close interval surveillance. See Video Abstract.