BTK and B-cell chronic lymphocytic leukemia: For example, retained anti-IgM signaling capacity is associated with progressive disease (6), and kinase inhibitors (KI) targeted against BCR signaling pathways, especially the Bruton tyrosine kinase (BTK) inhibitor ibrutinib, can induce impressive clinical responses in patients with CLL and some subtypes of non–Hodgkin lymphoma (7–9).