PDCD1 and metastatic melanoma: Tumor‐derived T‐cell immunotherapy, a cellular therapy, was recently approved by the US Food and Drug Administration in patients with unresectable or metastatic melanoma who have previously received other therapies such as anti–PD‐1 therapy, and in patients with tumors that are BRAF V600 mutation positive, a BRAF inhibitor with or without a mitogen‐activated protein kinase (MEK) inhibitor.31