Organ-preservation in rectal cancer: What is at risk when offering watch and wait for a clinical complete response? Data from 2 international registries in rectal cancer.
Authors: Fernandez Laura Melina , São Julião Guilherme Pagin , Vailati Bruna Borba , Santacruz Carlos Cerdan , Renehan Andrew , Beets Geerard , Habr-Gama Angelita , Azevedo José Moreira , Parvaiz Amjad , Perez Rodrigo O. 
Published: January 2024

7 Background: Organ-preservation has become an attractive alternative to total mesorectal excision (TME) among patients with rectal cancer following neoadjuvant therapy. Patients who achieve a clinical complete response (cCR) are currently offered watch-and-wait (WW) without immediate resection. Nearly 30% of these patients will develop local regrowth usually within 3 years from initial decision to WW. While salvage resection is frequently feasible, keeping the primary tumor in situ (despite clinically undetectable) may contribute to the risk for development of subsequent distant metastases (DM). The aim of the present study is to compare the risk of DM between patients with local regrowth (LR) after WW (undetectable residual disease) and patients with near-complete pathological response managed by TME at time of reassessment of response. Methods: Data from patients with rectal cancer following neoadjuvant therapy entered a prospective international database (IWWD) with cCR managed by WW and subsequent LR were compared to patients managed by TME from a prospectively maintained national registry (VIKINGO project). Near-complete response was defined at the presence of ≤10% residual cancer cells in the resected specimen. Primary endpoint was DM-free survival at 3 years from decision to WW or TME. Cox-logistic regression was performed to search for predictors of DM development. Kaplan-Meier curves were used to compare DM-free survival between groups based on statistically significant features found at multivariate analysis (p≤0.05) using log-rank test. Results: 508 patients with LR were compared to 893 patients with near-complete response after TME. Overall, DM rate was significantly higher among local regrowths (22.8% vs. 10.2%,; p≤0.001). Independent risk factors for DM included LR (versus TME at reassessment; p=0.001), ypT3-4 status (p=0.016) and ypN+ status (p=0.001) at the time of surgery. 3yr-DM-free survival was significantly worse for patients with local regrowth (75% vs. 87%; p=0.001). When stratified for pathological stage, patients with local regrowth did significantly worse through all stages ypT1-2N0 (p<0.001); ypT3-4N0 (p=0.009) and ypTanyN+ (p<0.001). Conclusions: Development of LR following WW is a significant and independent risk factor for subsequent DM. Final pathological stage is also a risk factor for subsequent DM. Patients with local regrowth have a higher risk for subsequent DM development than patients managed by TME at restaging irrespective of final ypT and ypN status. Leaving the primary undetectable tumor in situ until development of local regrowth may result in worse oncological outcomes. Future studies incorporating organ-preservation strategies should focus on the subsequent risk of DM among patients who eventually develop local regrowth as one of clinically relevant primary endpoints.