Induction immunochemotherapy conversion rate and survival outcomes versus chemotherapy in initially unresectable esophageal squamous cell carcinoma.

e16077 Background: Currently, no comparative study has been reported to elucidate whether the addition of immunotherapy in the induction setting could improve treatment efficacy and prolong the overall survival of initially-unresectable locally advanced esophageal squamous cell carcinoma (iuESCC). This study aimed to compare surgical conversion rate and short-term overall survival in induction chemotherapy (iC) and induction immunochemotherapy (iIC) for patients with iuESCC. Methods: In this multicenter retrospective cohort study, patients with the guideline-defined unresectable disease were included at four high-volume institutions. The primary endpoints were conversion surgical rate and overall survival (OS). Pathological complete response (pCR) was defined as the disappearance of tumor cells in the primary lesion site. Multivariate cox regression analysis was used to identify the independent significant prognostic factors associated with OS. The stabilized inverse probability of treatment weighting (IPTW) was applied to confirm the survival comparison between iIC and iC cohorts. Results: A total of 309 patients (150 in iIC and 159 in iC cohort) were included. A significantly higher conversion surgical rate was observed in iIC cohort (iIC vs. iC: 127/150, 84.7% vs. 79/159, 49.7%, P < 0.001). In terms of pathological response, the rates of pCR were 22.0% and 5.1% in the iIC and the iC cohort, respectively (P = 0.001). A significant difference in OS was observed between iIC (not reached) and iC cohorts (median [95% CI]: 36.3 [27.2 – 45.5] months). The stabilized IPTW yielded similar results. Regimen (iIC vs. iC, HR 0.215, 95% CI: 0.102 - 0.454, P < 0.001) and operation (Yes vs. No, HR 0.262, 95% CI: 0.161 - 0.427, P < 0.001) were the significant prognostic factors for OS. Further, subgroup analysis revealed that significantly higher OS was seen in iIC cohort than that in the iC cohort (P = 0.003) in patients who had non-pCR disease. Conclusions: Immunochemotherapy plus conversion surgery in the induction setting had higher pathological response rate and better OS in iuESCC patients. Moreover, this combined modality also contributed to improving OS in patients with residual tumor burden. This study provided evidence for future randomized control trial designs.