Both BTK and HCK are targets of ibrutinib, a pleiotropic kinase inhibitor that is active in patients with MYD88-mutated B-cell malignancies, including Waldenstrom’s macroglobulinemia (WM), ABC subtype of diffuse large B-cell lymphoma (DBLCL), and primary CNS lymphoma (PCNSL)7–10. The gene discussed is HCK; the disease is primary central nervous system lymphoma.