ROS1 and neoplasm: PD-L1 IHC is performed systematically by most laboratories for administration of first-line pembrolizumab therapy, even before obtaining the results of the genetic status of EGFR, ALK, ROS1 and BRAF. Only patients without mutations in these four genes and showing expression of PD-L1 in more than 50% of tumor cells are eligible for treatment with pembrolizumab [63].