Ibrutinib: a new frontier in the treatment of chronic lymphocytic leukemia by Bruton's tyrosine kinase inhibition.

Chronic lymphocytic leukemia (CLL) is characterized by progressive accumulation of nonfunctional mature B cells in blood, bone marrow and lymphoid tissues. In the last decade, our understanding of CLL and consequently our diagnostic and therapeutic approaches have changed dramatically. Conventional fludarabine based chemotherapy has led to improved disease response and longer survival in young patients with CLL. However its application in elderly patients has been restricted by substantial myelosuppression and infection. Treatment of CLL is now moving towards targeted therapy. The success of new class of agents such as monoclonal antibodies, proteasome inhibitors and immunomodulatory derivatives has sparked further search for treatment agents with novel targets to inhibit. The B cell receptor activating pathway involving the Bruton's tyrosine kinase (BTK) is crucial in B cell production and maintenance and is an attractive therapeutic target. Ibrutinib is an oral covalent inhibitor of the BTK pathway that induces apoptosis of B cells. Early phase studies with Ibrutinib either as a single agent or in combination regimens have shown promising results with an excellent safety profile in patients with high-risk, refractory or relapsed CLL and elderly treatment-naïve patients. This review summarizes the current knowledge of Ibrutinib in the treatment of CLL.