CD8A and cancer: CD8+ T-cell infiltration in tumor (Tumeh et al., 2014), high tumor mutational burden (Mehnert et al., 2016; Panda et al., 2017), exogenous viral infection in tumor (Kwong et al., 2017; Carbone et al., 2018; Panda et al., 2018b), and expression of endogenous retrovirus in tumor (Panda et al., 2018a) are associated with immune activation and checkpoint pathway upregulation in many cancer types, and response to immune checkpoint blockade in several cancer types.