Abstract 4025: A phase II trial of neoadjuvant gemcitabine, cisplatin plus tislelizumab followed by concurrent chemoradiotherapy in locoregionally advanced nasopharyngeal carcinoma: Clinical efficacy, safety and the biomarker analysis

Abstract Immune checkpoint inhibitors (ICIs) have been widely used in recurrent or metastatic nasopharyngeal carcinoma (NPC), but the addition of ICIs to chemoradiotherapy in locoregionally advanced (LA) NPC requires further investigation. We conducted a phase II, single-arm trial to evaluate the efficacy and safety of neoadjuvant gemcitabine, cisplatin (GP) plus tislelizumab followed by concurrent chemoradiotherapy (CCRT) in LA-NPC. All participants received 3 cycles of GP chemotherapy plus tislelizumab (200 mg) followed by 3 cycles of cisplatin-based CCRT. The primary endpoint was the clinical complete response rate (CR) after neoadjuvant chemoimmunotherapy (NAT). The secondary endpoints include pathological CR rate, progression-free survival (PFS), overall survival (OS), locoregional relapse-free survival (LRRFS), distant metastasis-free survival (DMFS), etc. Pretreatment blood samples and paired (pre-/post-NAT) tissue biopsies were collected to perform full-spectrum peripheral T-cell profiling, PD-L1 and tertiary lymphoid structures (TLS) staining. Among all 63 participants, the CR rate after NAT reached 41.3% (95% CI, 28.8%-53.8%), far exceeding our hypothesized CR rate of 22%. The objective response rate (ORR) and pCR rate after NAT were 88.9% (95% CI, 80.9% to 96.9%) and 74.6% (95% CI, 62.1% to 84.7%), respectively. As of July 15th, 2023, after the median follow-up of 25 months, the 2-year PFS and OS were 98.4% and 100%. The incidence of grade 3-4 immunotherapy-related adverse events was 1.6%. The compliance of CCRT was not compromised. Patients who achieved CR had significantly more circulating CD4+ and CD8+ effector memory T cells (Tem), regulatory T cells (Treg) and follicular helper T cells (Tfh). The peripheral abundance of LAG3+ Tem and Tfh were independently predictive of NAT response. The number and maturation of TLS significantly increased after NAT in the CR group, but not in the Non-CR group. GP chemotherapy plus tislelizumab followed by CCRT was highly therapeutic and safe in treating LA-NPC, further randomized phase III studies are awaited. Citation Format: Xiao-Yun Li, Si-Yi Xie, Qiu-Yan Chen, Hai-Qiang Mai, Lin-Quan Tang. A phase II trial of neoadjuvant gemcitabine, cisplatin plus tislelizumab followed by concurrent chemoradiotherapy in locoregionally advanced nasopharyngeal carcinoma: Clinical efficacy, safety and the biomarker analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4025.