CTLA4 and head and neck squamous cell carcinoma: For example, methylation of the PD-L1 promoter predicts survival in colorectal cancers, head and neck squamous cell carcinoma, and acute myeloid leukemia [64,65,66]; PD-1-promoter methylation is associated with recurrence-free survival in prostate cancer [65]; and CTLA-4 methylation correlates to response to anti-PD-1 and anti-CTLA-4 immunotherapy in melanoma [67].