Ibrutinib in Treating Patients With Relapsed Hairy Cell Leukemia

PRIMARY OBJECTIVE: I. To determine the overall response rate (complete response \[CR\] and partial response \[PR\]) of hairy cell leukemia (HCL) at 32 weeks after beginning therapy with single-agent ibrutinib. SECONDARY OBJECTIVES: I. To characterize the toxicity and tolerability of single-agent ibrutinib when administered to patients with HCL. II. To characterize the progression-free (PFS) and overall survival (OS) of single-agent ibrutinib when administered to patients with HCL. III. To determine the rate of molecular remission (minimal residual disease \[MRD\]-negative CR) among all patients, defined as resolution of all detectable disease below the limits of detection by immunohistochemistry and/or 4-color flow cytometry assay at 32 weeks after beginning ibrutinib therapy. IV. To characterize immunologic outcomes during single agent ibrutinib administration. V. To explore the effect of ibrutinib (PCI-32765) on traditional and new biomarkers in HCL including: Va. Confirmation of expression BRAFV600E in leukemia cells Vb. Pharmacodynamic effects of BTK inhibition on phosphorylated (phospho) ERK regulation, as well as other potential protein kinase targets of ibrutinib (exploratory) Vc. Serum soluble IL-2 receptor correlation with response to ibrutinib therapy Vd. Documentation of and quantification of minimal residual disease following maximal response, with flow cytometric analysis and immunohistochemical stains of the bone marrow, as predictors of remission duration after ibrutinib therapy. OUTLINE: Patients receive ibrutinib orally (PO) once daily (QD) on days 1-28. Cycles repeat every 28 days for up to 8 cycles if lack of response to therapy, up to 12 cycles if failure to achieve an objective response (CR/PR), or continually at per physician discretion in the absence of disease progression or unacceptable toxicity. Additionally, patients undergo bone marrow aspiration and biopsy, blood sample collection, and computed tomography (CT) or ultrasound throughout the study. After completion of study treatment, patients are followed up every 3 months.