Recent clinical data suggest remarkable activity of ibrutinib, the 
first-in-class covalent inhibitor of Bruton's tyrosine kinase (BTK), in chronic 
lymphocytic leukemia (CLL), as well as excellent activity in other B cell 
malignancies, including in particular mantle cell lymphoma and Waldenstrom 
macroglobulinemia. This review evaluates the data from ongoing clinical and 
correlative studies of ibrutinib in B cell malignancies with a particular focus 
on CLL, and considers these data in the context of other B cell receptor pathway 
inhibitors.