Exosome concentrations were decreased in CLL patients after receiving ibrutinib therapy. Exosomes were isolated from plasma collected before (cycle 1, day 1) and after ibrutinib treatment (cycle 2, day 1) in a phase 2 clinical trial (OSU-11133; #NCT01589302). Plasma exosome concentration in CLL patients after receiving ibrutinib therapy was significantly reduced compared with pretreatment (P = .05).