Long-term follow-up results of a pivotal trial involving moxetumomab pasudotox indicated durable responses for patients with relapsed/refractory (R/R) hairy cell leukemia (HCL) who had received this agent after 2 or more prior lines of therapy. The trial results were published in the Journal of Hematology & Oncology.

In this multicenter, single-arm trial (ClinicalTrials.gov Identifier: NCT01829711), patients were required to have received prior systemic therapies that included 2 or more purine nucleoside analog (PNA) courses or 1 course of a PNA followed by rituximab or a BRAF inhibitor. Patients were given moxetumomab pasudotox intravenously at 40 mg/kg for up to 6 cycles on days 1, 3, and 5 of each 28-day cycle. The primary study endpoint was the rate of durable complete response (CR), which was defined as CR with hematologic remission lasting more than 180 days. Response and minimal residual disease (MRD) results were evaluated through blinded independent central review.

A total of 80 patients received moxetumomab pasudotox, with 63% completing all 6 cycles. The median number of prior therapies was 3. Nearly half (49%) of all patients were refractory to PNAs, and 38% of patients were found unfit for retreatment with a PNA.

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The median study follow-up was 24.6 months. The rate of durable CR, the primary endpoint, was 36% (95% CI, 26%-48%). CR with hematologic recovery of 360 or more days was reported in 33% or patients. The overall CR rate was 41% and the objective response rate was 75%.

Most (82%) of the complete responders demonstrated MRD-negativity, which amounted to 34% of the total patient population. The rate of CR lasting 60 months or more was 61%, and the median duration of CR was 62.8 months. The median progression-free survival was 41.5 months if a progression event included the loss of any CR criterion, and it was 71.7 months if an event also required a loss of hematologic remission.

Nearly all (99%) of the patients had 1 or more adverse events. The most common grade 3 or 4 adverse events were decreased lymphocyte count (20% of patients), anemia (10%), and asymptomatic hypophosphatemia (10%). A total of 4 fatalities occurred by the median study follow-up, with 2 related to disease progression, 1 due to pneumonia, and 1 from septic shock.

“The results of this trial represent an important step forward for patients with R/R HCL, providing a clinically meaningful option following initial treatment with a PNA,” the study investigators concluded in their report.

Disclosures: Some authors have declared affiliations with or received grant support from the pharmaceutical industry. Please refer to the original study for a full list of disclosures.


Kreitman RJ, Dearden C, Zinzani PL, et al. Moxetumomab pasudotox in heavily pre‑treated patients with relapsed/refractory hairy cell leukemia (HCL): long‑term follow‑up from the pivotal trial. J Hematol Oncol. 2021;14(1):35. doi:10.1186/s13045-020-01004-y