The Current Landscape of Immune Checkpoint Blockade in Metastatic Lung Squamous Cell Carcinoma

In addition to surgery, chemotherapy, radiotherapy, and targeted therapy, immunotherapy has emerged as a standard pillar of cancer treatment. Immune checkpoint inhibitors (ICIs) such as targeting programmed death-1/programmed death ligand 1 (PD-1/PD-L1) and cytotoxic T lymphocyte antigen 4 (CTLA-4) have been integrated into standard-of-care regimens for patients with advanced lung squamous cell carcinoma (LUSC), who were previously limited by the lack of treatment options. Atezolizumab, durvalumab, nivolumab, and pembrolizumab are all currently used as part of standard-of-care treatment for different stages of lung cancer. Recent successes and failures of immune checkpoint blockade-based combination therapies have provided significant insights into implementing combination strategies in LUSC. Therefore, there is an urgent need to correctly select patients who are more likely to respond to immunotherapy and understand the mechanisms of primary or acquired resistance. In this review, we aim at summarizing the emerging clinical data on the promise and challenge of ICIs, discussing the unmet need of potential biomarkers for predicting response or resistance to immunotherapy, and providing an overview of the current immune landscape and future directions in advanced LUSC.