PDCD1 and plasma cell myeloma: examined the roles of the PD-1/PD-L1 pathway in tumor immunity and found that myeloma growth in mice was significantly inhibited by anti-PD-L1 treatment or PD-1 deficiency, indicating that PD-L1 expression may allow tumors to escape from the host immune system and that the blockade of the PD-1 and PD-L1 axis may represent an effective strategy for cancer treatment (51).