2013 - Accuracy of Restaging after TNT to Predict Final Treatment Response Among Locally Advanced Rectal Cancer Patients Receiving Short Course Radiation

Purpose/Objective(s): Recent studies have demonstrated that cure without surgery is achievable in up to half of patients with locally advanced rectal cancer (LARC) treated with total neoadjuvant therapy (TNT). A key challenge is accurately assessing post-TNT tumor response to appropriately select patients for nonoperative management. We sought to determine the accuracy of clinical and radiologic restaging in predicting final treatment response in patients treated with TNT incorporating short course radiation.

Materials/Methods: We performed a retrospective review of 44 patients treated with TNT using short course radiation therapy (25 Gy in 5 fractions) from 2016-2025 at a single institution. Demographic, treatment, restaging, post-operative pathologic response, local and distant recurrence and survival data were collected. Restaging assessment included radiologic (MRI, CT, PET/CT) and/or clinical (endoscopic) assessments. Final tumor response was determined by post-operative pathology results for those undergoing surgery or incidence of local or distant recurrence 12 months after restaging in patients pursuing nonoperative management.

Results: The population consisted of 26 men and 18 women with a mean age of 61.41 years (range 27-85). Approximately 70% had T3 and 50% had N1 disease. For restaging, 79.5% had an MRI and 61.4% had flexible sigmoidoscopy. Two-thirds of patients underwent surgical resection, most commonly low anterior resection, and one-third pursued non-operative management. Average time from TNT to restaging was 35.29 days. The sensitivity, specificity and accuracy of combined restaging (radiologic and clinical) in determining final treatment response were 92.59%, 47.06% and 75%. The specificity for patients who had combined restaging performed 40 days or less after TNT completion compared to more than 40 days after TNT completion was 40% vs 66.67%.

Conclusion: Combined clinical and radiologic restaging after TNT with short course radiation in LARC patients is highly sensitive but lacks specificity. As a result, surgery was recommended to over half of patients after TNT with short course radiation who may have achieved cure with organ preservation. While not statistically significant, there was a trend toward increased specificity of restaging when the time interval from TNT completion to restaging occurred more than 40 days after TNT, suggesting that extending the interval to restaging may reduce resection rates while maintaining oncologic outcomes. Future studies with larger patient cohorts could help delineate this difference.