2187 - Induction Chemoimmunotherapy vs. Induction Chemotherapy followed by Definitive Radiotherapy in Esophageal Squamous Cell Carcinoma: An Observational Study on Efficacy and Factors Associated with Better Outcomes

03:00pm - 04:00pm ET

Poster Hall - Exhibit Hall A

Screen: 24

POSTER

Presenter(s)

Xuejiao Ren, MD, PhD - Department of Radiation Oncology, the Fourth Hospital of Hebei Medical University, Shijiazhuang, Hebei Province

X. Ren¹, X. Fan², L. Liu¹, C. Han¹, and L. Wang¹; ¹Department of Radiation Oncology, the Fourth Hospital of Hebei Medical University, Shijiazhuang, Hebei Province, China, ²Department of Radiation Oncology, The Fourth Hospital of Hebei Medical University, Shijiazhuang, Hebei, China

Background: Induction chemoimmunotherapy or chemotherapy before definitive radiotherapy is increasingly used for surgically unresectable esophageal squamous cell carcinoma (ESCC), yet its benefits remain unclear.

Purpose/Objective(s): To compare the efficacy and safety of induction chemoimmunotherapy (IIC+RT) versus induction chemotherapy (IC+RT) followed by definitive radiotherapy in surgically unresectable ESCC and identify prognostic factors.

Materials/Methods: This retrospective study included 241 patients with surgically unresectable ESCC treated from 2020 to 2023 (IIC+RT:130, IC+RT:111). Inverse probability of treatment weighting (IPTW) balanced baseline covariates. Survival was analyzed using Kaplan-Meier and Cox regression.

Results: For the entire cohort, the 1- , 3- , and 5- year OS rates were 84.0%, 53.4%, and 45.2%, respectively (median 38.3 months); the corresponding rates for PFS were 68.1%, 34.3%, and 30.5% (median 20.8 months), and for LC were 85.7%, 68.8%, and 68.8%. After IPTW adjustment, no significant differences were observed between the IIC+RT and IC+RT groups (OS: HR=0.74, P=0.170; PFS: HR=0.75, P=0.116; LC: HR=0.57, P=0.064). Within the IIC+RT group, concurrent immunotherapy significantly improved PFS (HR=0.54, P=0.026; 5- year PFS 43.0% vs. 18.8%) but not OS. Multivariable analysis identified post- induction tumor response as an independent prognostic factor for OS, PFS, and LC in the IIC+RT group (all P<0.05), whereas post- radiotherapy response independently predicted outcomes in the IC+RT group (all P<0.05). Notably, patients in the IIC+RT group who did not achieve objective response after induction had the poorest prognosis, with 5- year OS and PFS of only 28.6% and 17.4%, significantly inferior to responders in either the IIC+RT (48.7% and 40.8%) or IC+RT group (57.9% and 52.2%) (all P<0.05). Regarding safety, the IIC+RT group had significantly higher rates of adverse events during radiotherapy, including anemia (P=0.043), liver dysfunction (P=0.016), grade =3 radiation esophagitis (P=0.016), and grade =3 pneumonitis (P=0.038). Treatment- related mortality occurred in 7 patients (5.4%) in the IIC+RT group (with 4 esophageal fistulas and 3 pneumonitis) compared to 1 patient (0.9%) in the IC+RT group (P=0.097).

Conclusion: In patients with surgically unresectable ESCC receiving induction therapy followed by definitive radiotherapy, the addition of immunotherapy did not improve overall survival and was associated with increased toxicity. While concurrent immunotherapy improved PFS, this did not translate into an OS benefit. Post- induction tumor response emerged as a critical prognostic determinant in the IIC+RT strategy, whereas post-radiotherapy response better predicted outcomes in the IC+RT approach. These findings underscore the need for careful patient selection and prospective validation.

Keywords: Esophageal squamous cell carcinoma; Induction chemoimmunotherapy; Definitive radiotherapy; Prognostic factors