Moxetumomab Pasudotox for Advanced Hairy Cell Leukemia

Background: \- Moxetumomab pasudotox is an experimental non-chemotherapy cancer treatment drug. It targets CD22, a molecule on the surface of essentially all hairy cell leukemia cells. Moxetumomab pasudotox binds to CD22, goes into the cell, and releases a toxin which kills the cell. In a phase I trial it had activity in relapsed/refractory hairy cell leukemia with safety profile supporting further clinical study (http://ncbi.nlm.nih.gov/pubmed/22355053). This is a phase III multicenter trial designed to confirm these results.

Background: * Hairy cell leukemia (HCL) is an indolent B-cell leukemia comprising 2% of all leukemias, or approximately 900 of the 44,000 new cases of leukemia/year in the US * Over the last two decades, immunotoxin research has accumulated to support a role for CD22-targeted therapy in the treatment of HCL. * Moxetumomab pasudotox is a recombinant immunotoxin containing an Fv fragment of an anti-CD22 monoclonal antibody and truncated Pseudomonas exotoxin. * Moxetumomab pasudotox has demonstrated a high complete response (CR) rate in patients with chemoresistant HCL and has shown activity in pediatric acute lymphoblastic leukemia as well. * Modification of the structure of moxetumomab pasudotox has greatly improved binding and cytotoxicity toward CD22 expressing malignant cells compared to the precursor molecule. Preclinical and clinical studies have demonstrated that this increase in binding affinity results in improved antitumor activity and tolerability * Currently there are no approved agents with significant efficacy for HCL patients after failure of standard therapy Design: * This is a multicenter, single-arm study of moxetumomab pasudotox in patients with relapsed/refractory hairy cell leukemia. * 77 patients will be enrolled to receive moxetumomab pasudotox intravenously (IV) on days 1, 3 and 5 of each 28 day cycle for a maximum of 6 cycles or until disease progression, unacceptable toxicity occurs, the subject begins alternate therapy, or documented CR (for subjects who have no assessable minimal residual disease and not to exceed 6 cycles). If less than or equal to 2 of the first 25 patients do not achieve durable CR, no additional patients will be accrued. * The overall IRB accrual ceiling is currently set at 80 to allow for a small number of patients that cannot be assessed for response.