IFNG and neoplasm: However, up to 20% of PD−L1−negative malignancies showed responses to PD−1 inhibitors in some cohorts (103), as PD-L1 expression can be up-regulated by other factors including activated IFN-γ cascade (will be discussed in a separated part), suggesting tumor PD-L1 expression alone is not dependable at predicting outcomes of PD-1/PD-L1 inhibitors.