Allele-specific polymerase chain reaction assays were used to detect MYD88 L265P. CXCR4 mutational status was determined by Sanger sequencing...At best response, 2 patients attained partial response (PR), 1 attained minor response, and 3 had stable disease (SD), and 7 experienced progressive disease, for an ORR of 23%, major response rate of 15%, and clinical benefit of 54%....Baseline CD38 expression was higher in plasma cells than in B cells (MFI, 18 048 and 2574, respectively; P < .001)....Our findings suggest that response to daratumumab might be impacted by baseline CD38 expression in plasma cells...