PDCD1 and cancer: Six antibodies targeting the PD1/PDL1 axis have already been approved by the US Food and Drug Administration (FDA) for clinical use in several cancer settings and numerous others are currently under clinical development (Gong et al. 2018; Jiang et al. 2020; Vaddepally et al. 2020; Waldman et al. 2020; Twomey and Zhang 2021; Parvez et al. 2023).