Mechanisms of primary resistance to immune checkpoint inhibitors in NSCLC

Immune checkpoint inhibitors (ICIs) redefined the therapeutics of non-small cell lung cancer (NSCLC), leading to significant survival benefits and unprecedented durable responses. However, the majority of the patients develop resistance to ICIs, either primary or acquired. Establishing a definition of primary resistance to ICIs in different clinical scenarios is challenging and remains a work in progress due to the changing landscape of ICI-based regimens, mainly in the setting of early-stage NSCLC. The mechanisms of primary resistance to ICIs in patients with NSCLC include a plethora of pathways involving a cross-talk of the tumor cells, the tumor microenvironment and the host, leading to the development of an immunosuppressive phenotype. The optimal management of patients with NSCLC following primary resistance to ICIs represents a significant challenge in current thoracic oncology. Research in this field includes exploring other immunotherapeutic approaches, such as cancer vaccines, and investigating novel antibody–drug conjugates in patients with NSCLC.