CD38 and plasma cell myeloma: Daratumumab, a human IgGκ monoclonal antibody targeting CD38 with a direct on-tumor [1–4] and immunomodulatory [5–7] mechanism of action, is approved in many countries as monotherapy for relapsed or refractory multiple myeloma (RRMM) patients and in combination with standard-of-care regimens for RRMM and newly diagnosed multiple myeloma (NDMM) patients [8–17].