Immune checkpoint inhibitors in esophageal squamous cell carcinoma: progress and opportunities

Esophageal squamous cell carcinoma (ESCC) is one of the common malignant tumors in the world. More than half of patients with ESCC were detected in advanced or metastatic disease at the time of initial diagnosis and lost the opportunities of surgery. Currently, surgical resection, radiotherapy, and chemotherapy are most utilized in clinical practice, however, they are associated with limited survival benefits. Recognition of the limitation of traditional antitumor strategies prompt the development of new means to treat human cancer. In recent years, studies on immune checkpoint inhibitors (eg PD-1/PD-L1 inhibitors, CTLA-4 inhibitors, etc.) in ESCC have shown promising results. In addition, the combination of immune checkpoint inhibitor and traditional antitumor strategies for ESCC has caused extensive interest, and the results are encouraging. Previous analysis indicated that tumor cell PD-L1 expression, tumor mutation load (TMB), microsatellite instability-high status (MSI-H), and other biomarkers have relatively correlated with the efficacy of immunotherapy. This review explores the recent studies investigating checkpoint inhibitors in ESCC.