However, unlike other tumor types such as lung or head & neck cancer, where PD-L1 expression by immunohistochemistry (IHC) is used to guide patient stratification to ICI treatment, PD-L1 expression by IHC has not been proven to be a reliable predictive biomarker in melanoma, as evidenced by exploratory analyses of large scale studies [130,131,132]. This evidence concerns the gene CD274 and melanoma.