PDCD1 and plasma cell myeloma: Some antibodies, such as nivolumab (anti‐PD‐1), pembrolizumab (anti‐PD‐1), and ipilimumab (anti‐CTLA‐4), have been approved by the US FDA and have shown excellent therapeutic effect on melanoma, nonsmall cell lung cancer, glioblastoma, large B‐cell lymphoma, multiple myeloma, renal cell carcinoma, and so on.7, 8, 9, 10