PDCD1 and melanoma: Blocking this checkpoint by PD-1 inhibitors has resulted in impressive clinical response rates in melanoma (Roboz et al., 2014) and non-small cell lung cancer (Giroux Leprieur et al., 2017), as well as in Hodgkin (Le et al., 2015; Armand et al., 2018) and non-Hodgkin lymphomas (Lesokhin et al., 2016).