CTLA4 and melanoma: In melanoma cells resistant to combined anti‐CTLA4 and radiation treatment, they have elevated PD‐L1 expression.16 CD4+ T cells from bladder cancer patients receiving anti‐CTLA4 treatment had markedly increased production of IFN‐γ.17 IFN‐γ is known to induce PD‐L1 expression.18 Oncogenic EGFR activation has been found to up‐regulate PD‐1 and PD‐L1.19, 20 PD‐L1 expression was associated with adenocarcinoma and EGFR mutations.14