IL-6 and IL-10 cytokine levels in MYD88-mutated WM patient sera following ibrutinib treatment. The (A) IL-6 and (B) IL-10 cytokine levels were detected by ELISA in MYD88-mutated WM patients with acquired BTK^Cys481Ser mutation and progressed on ibrutinib as well as patients with BTK^WT and continued response to ibrutinib. Blue arrows indicate ibrutinib start date. Red arrows indicate date at BTK^Cys481 mutations were first noted in patients with disease progression, whereas green arrows show determination point for BTK wild-type status for those patients with ongoing response. All patients achieved a major response, and their clinical course and determination of BTK mutation status were previously reported.⁸