Putative predictors of efficacy for immune checkpoint inhibitors in non-small-cell lung cancer: facing the complexity of the immune system.

In non-small-cell lung cancer (NSCLC) the recent introduction of immunotherapy in daily clinical practice produced a wave of enthusiasm, however, this was rapidly moderated by the evidence that only some patients could experience a relevant clinical benefit. Therefore, a great effort from the scientific community has been dedicated to the identification and validation of reliable biomarkers able to drive the activity of immunotherapeutic agents. Areas covered: This analysis aims to review the main findings about predictive biomarkers for immunotherapy in lung cancer, retracing the history of PD-L1 and focusing on a series of innovative candidates, such as mutational load, immune cell populations and microbiome. Expert commentary: Considering the complexity of the immune system-cancer interactions, the idea of identifying a single biomarker able to drive the activity of different immunotherapeutic agents alone, borrowing the idea of targeted therapy, is likely to represent an unrealistic objective. Nevertheless, the identification of those factors either positively or negatively affecting the response is mandatory in order to recruit the appropriate patients, but also to deeply understand the mechanisms of immune response and improve the clinical benefit deriving from these agents in monotherapy or in a biologically-rationale combination.