HSPA4 and B-cell chronic lymphocytic leukemia: In addition, Hsp70 has been determined to be involved in the resistance to ibrutinib, an inhibitor of Bruton’s tyrosine kinase (Btk) in chronic lymphocytic leukemia (CLL), as shown in vitro on leukemic cells obtained from untreated patients and those in which the ibrutinib treatment failed [154].