Bruton's tyrosine kinase (Btk) is an enzyme that is present in hematopoietic cells other than T cells and is necessary for downstream signal transduction from various hematopoietic receptors including the B cell receptor as well as some Fc, chemokine, and adhesion receptors, and is crucial for both B cell development and osteoclastogenesis. Although down-regulated in normal plasma cells, Btk is highly expressed in the malignant cells from many myeloma patients and some cell lines. PCI-32765 is a potent and specific inhibitor of Btk currently in Phase 2 and 3 clinical trials. The current study is designed and intended to determine the safety and efficacy of PCI-32765 in combination with carfilzomib (Kyprolis™) with and without dexamethasone in subjects with relapsed or relapsed and refractory multiple myeloma (MM).
