PD-L1 as a prognostic and predictive biomarker in neuroendocrine tumors of the lung: state of the art and future perspectives

Neuroendocrine tumors (NETs) of the lung are a heterogeneous group of neoplasms with different biological and clinical features. Immunotherapy with checkpoint inhibitors (ICIs) targeting the PD-1/PD-L1 axis, has been introduced in the last years as a novel treatment option in many cancer types, and results from recent trials showed survival benefit for immunotherapy alone or combined with chemotherapy in high-grade NETs, especially small cell lung cancer (SCC). However, defined biomarkers to select patients who are more likely to benefit from ICIs are currently lacking. On the other hand, there is also significant, although heterogeneous evidence of a prognostic role of PD-L1 status in NETs of the lung. Aim of this review was to summarize the current knowledge about the prognostic and predictive value of PD-L1 expression in NETs of the lung, and to discuss its inherent technical issues and clinical implications.