CD38 and plasma cell myeloma: Many hematological malignancies, such as multiple myeloma, T cell acute lymphoblastic leukemia (ALL), peripheral T cell lymphoma [30], and B cell ALL, express CD38 [31–33]; however, most solid tumors lack tumor-intrinsic expression of CD38, with the exception of certain prostate tumors [34] and lung tumors, where upregulation of CD38 has been associated with resistance to programmed cell death protein/ligand-1 therapy [35,36].