Tumor microenvironment-directed novel checkpoint strategies in esophageal squamous cell carcinoma: a narrative review on current status and limitations

Abstract

Background and Objective: The current treatment landscape for advanced or metastatic esophageal squamous cell carcinoma (ESCC) has been reshaped by immune checkpoint inhibitors (ICIs) targeting programmed cell death protein 1 (PD-1), programmed death-ligand 1 (PD-L1), and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), major coinhibitory pathways regulating antitumor T cell responses. Improved efficacy and survival have been observed with PD-1 and PD-L1 combination therapies, which supports the exploration of additional immune checkpoints as therapeutic targets in ESCC. This review summarizes emerging immune checkpoint strategies that are mechanistically relevant to ESCC, including CTLA-4 targeted by novel approaches with potentially improved therapeutic index, exhaustion-directed pathways such as LAG-3, TIM-3, and TIGIT, and regulatory T-cell-mediated immune exclusion.Methods: We searched abstracts and proceedings from PubMed, major oncology meetings, as well as ClinicalTrials.gov from January 2016 to April 2026 to identify published studies on the tumor microenvironment-directed novel checkpoint in ESCC, with language restrictions (English).Key Content and Findings: We highlight how antibody format and clinical context shape activity, including tumour-localized or conditionally active anti-CTLA-4 antibodies designed to improve tolerability, the context-dependent performance of TIGIT blockade across treatment settings, and microenvironment-directed strategies targeting profound T cell exhaustion.Conclusions: Available clinical evidence suggests that empiric first-line intensification in unselected populations may yield limited incremental benefit, whereas mechanism-matched and biomarker-enriched strategies, particularly in anti-PD-1/PD-L1-refractory disease, may represent a more rational development path. Well-designed translational studies incorporating prospective clinical trials, rigorously collected biospecimens, and advanced investigational platforms may help guide the next phase of development for immunotherapy in ESCC.