PD‐L1 and beyond: Immuno‐oncology in cytopathology

Over the past decade, immunotherapy has emerged as one of the most promising cancer treatments. Several monoclonal antibodies targeting the programmed death 1 (PD‐1)/ programmed death ligand‐1 (PD‐L1) pathway have been integrated into standard‐of‐care treatments for a wide range of cancer types. Although all the available PD‐L1 immunohistochemistry (IHC) assays have been developed on formalin‐fixed histological specimens, a growing body of research has recently suggested the feasibility of PD‐L1 testing on cytological samples. Although promising results have been reported, several important issues still need to be addressed. Among these are pre‐analytical issues, cyto‐hystological correlation, and inter‐observer agreement. This review will briefly summarise the knowledge gaps and future directions of cytopathology in the immuno‐oncology scenario.