CD38 and plasma cell myeloma: It has been observed that macrophages associated with myeloma (MAMs) display a defective vitamin D pathway; since vitamin D increases CD38 expression on plasma cells, enhancing binding of CD38-targeting antibodies, the ability of lenalidomide and pomalidomide to restore the vitamin D pathway explains the synergistic effect of lenalidomide and vitamin D in enhancing the efficacy of MAM-mediated cytotoxicity, and poses an important rationale for vitamin D supplementation during therapy with anti-CD38 and immunomodulatory drugs [106].