396. SHORT-TERM REVIEW: REAL-WORD EXPERIENCE OF PEMBROLIZUMAB AS FIRST-LINE CHEMOTHERAPY FOR ADVANCED ESOPHAGEAL SQUAMOUS CELL CARCINOMA

Abstract Background In Japan, Pembrolizumab, combined with standard chemotherapy (fluorouracil and cisplatin), was approved for first-line treatment of esophageal squamous cell carcinoma (ESCC) in November 2021. In advanced ESCC cases, modifications like omitting cisplatin or adding the palliative radiotherapy for malignant stenosis are sometimes necessary. The real-world application of Pembrolizumab with chemotherapy (Pem+C) in these scenarios remains uncertain. This review presents an overview of Pem+C’s short-term clinical outcomes in practice. Methods We retrospectively studied nineteen patients treated with Pem+C as the first-line chemotherapy for advanced ESCC from Nov. 2021 to Dec.2023. Response evaluation was primarily based on RECIST v1.1. Clinical worsening factored into some progression disease (PD) assessments. Adverse events were graded using CTC-AE v5.0. Kaplan-Meier survival curves were calculated by SPSS, with data cutoff on Dec. 31. 2023. Results Median age was 70 (49-83 years), PS (0/1/2):0/8/1, TPS (1≤/1≤/NE):1/2/16. Disease Status (Recurrence [locoregional/distant metastasis] /metastatic):3 [2/1] /16. Sequence of treatments (Pem+C alone/ concurrent palliative radiotherapy (pRT) consisting of 30-40Gy/ maintenance after chemoradiotherapy ):10/5/4. Three received only fluorouracil as backbone chemotherapy due to frailty. Median follow-up time, overall survival (OS) and progression free survival (PFS) were 8.3, 14.4, and 6.5 months, respectively. Responses in evaluable eighteen (CR/PR/nonCRnonPD/SD/PD):2/8/1/3/4. No unexpected severe adverse events (≥Grade3) were found. Among limited cases, concurrent pRT didn’t increased life-threatening AE; however, neutropenia ≥G3 seemed to be slightly frequent (2/5). One patient’s survival exceeded 24.8 months. Conclusion Our real-world experience with Pem+C in advanced ESCC includes diverse approaches clinical practices. The outcomes, while prelimiary, compare favorably with existing literature, without significant inferiority. The safety data and success case in the concurrent pRT group are significant, though limited by the small number of cases and short observation period. While further, more rigorous studies are necessary, adaptable Pem+C could be viable in practice.