Study of the Bruton's Tyrosine Kinase Inhibitor in Subjects With Relapsed or Relapsed and Refractory Multiple Myeloma

* Diagnosis of symptomatic MM with measurable disease, defined here as having at least one of the following: 1. Serum monoclonal protein (M-protein) ≥0.5 g/dL as determined by serum protein electrophoresis (SPEP) 2. Urine M-protein ≥200 mg/24 hrs 3. Serum free light chain (FLC) assay: involved FLC level ≥10 mg/dL (≥100 mg/L) provided serum FLC ratio is abnormal * Relapsed or relapsed and refractory MM after receiving at least 2 but no more than 5 previous lines of therapy, 1 of which must be an immunomodulator. * Refractory myeloma (to most recent treatment) is defined as disease that is nonresponsive while on treatment or progressive disease within 60 days after the completion of preceding treatment. Nonresponsive disease is defined as either failure to achieve minimal response or development of progressive disease while on therapy. * Men and women ≥18 years of age. * ECOG performance status of ≤ 1.

* Subject must not have primary refractory disease defined as disease that is nonresponsive in subjects who have never achieved a minor response (MR) or better with any therapy. * Polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes (POEMS) syndrome, osteosclerotic myeloma, or Crow-Fukase syndrome. * Plasma cell leukemia. * Primary amyloidosis. * Certain exclusions on prior therapy. * ANC \<0.75 x 10\^9/L independent of growth factor support. * Platelets \<50 x 10\^9/L) independent of transfusion support. * AST or ALT ≥3.0 x upper limit of normal (ULN). * Total bilirubin \>2.5 x ULN, unless due to Gilbert's syndrome. * Creatinine \>2.5 mg/dL. * Unable to swallow capsules or disease significantly affecting gastrointestinal function. * Requires anti-coagulation with warfarin or a vitamin K antagonist. Requires treatment with strong CYP3A4/5 inhibitors.