PDCD1 and melanoma: Since 2015, when the FDA approved combination immunotherapy with ipilimumab (anti-CTLA-4) and nivolumab (anti-PD-1) (Hellmann et al., 2019), the use of dual therapies has increased due to its higher efficacy than monotherapy against several cancers, including melanoma, non-small cell lung cancer, and colorectal cancer (Larkin et al., 2019; Baas et al., 2021; Overman et al., 2018).