CD38 and Miyoshi myopathy: Daratumumab is a human monoclonal antibody targeting CD38, a 45-kDa type II transmembrane glycoprotein that is highly expressed on MM cells.5 Daratumumab binds CD38 and induces tumor cell death through a direct on-tumor and immunomodulatory mechanism of action that consists of antibody-dependent cellular phagocytosis, complement-dependent cytotoxicity, antibody-dependent cell-mediated cytotoxicity, apoptosis, and clonal expansion of cytotoxic T cells.6–10