CD38 and plasma cell myeloma: Based on this observation and preclinical findings of better activity of daratumumab against myeloma cells both by complement-mediated cytotoxicity (CDC), antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) when the level of CD38 expression is high [8,11], it has been suggested that retreatment with daratumumab could be a reasonable strategy after a “wash-out” period of 3–6 months to allow for recovery of CD38 expression.