BTK and B-cell chronic lymphocytic leukemia: BTK inhibitor ibrutinib (PCI-32765) is one of the most recent FDA-approved drugs for refractory and aggressive 17p deleted form of CLL.73 XID mice bear a point mutation in Btk gene, which prevents its kinase activity.74 XID/TCL1 crossed mice have lower tumor burden in PB and superior survival than TCL1-tg.