BTLA and melanoma: Evaluation of melanoma data from The Cancer Genome Atlas (TCGA) revealed strong positive correlations between PDPN expression and several immune checkpoint receptors, including PD-L1, CTLA4, LAG3, TIGIT, and BTLA, with the association with PD-L1 (CD274) being the most prominent (r=0.504, p<0.001; Figure 1B).