NEW YORK – Ibrutinib, and now moxetumomab pasudotox, are two novel therapies that can be tried in patients with previously treated hairy cell leukemia, although data and experience with them are so far limited in this rare disease, experts said during a panel discussion at the National Comprehensive Cancer Network Hematologic Malignancies Annual Congress.
Since there are so few patients, data on the BTK inhibitor ibrutinib in hairy cell leukemia is largely “anecdotal,” said Andrew D. Zelenetz, MD, PhD, of Memorial Sloan Kettering Cancer Center in New York.
The anti-CD22 monoclonal antibody moxetumomab pasudotox – approved for hairy cell leukemia in September – isn’t yet on the formulary at Memorial Sloan Kettering, Dr. Zelenetz added in a panel discussion of treatment options for a patient previously treated with purine analogueues and vemurafenib.
Between the two agents, moxetumomab pasudotox has more robust data in this disease, said John N. Allan, MD, of Weill Cornell Medicine, New York.
“I think if you can get access to the drug, that’s probably the best answer,” Dr. Allan said in the case discussion.
Hairy cell leukemia is an indolent B-cell lymphoma that makes up just 2% of all lymphoid leukemias, according to NCCN guidelines.
It is a chronic disease that requires long-term management, according to Dr. Allan.
First-line treatment is usually a purine analogue, either cladribine or pentostatin, and multiple treatments are possible as long as responses of greater than 2 years are achieved, he told attendees at the NCCN conference.
For relapses more than 2 years after first-line treatment, patients can be retreated with the same purine analogue, with or without rituximab, or can be switched to the alternative purine analogue, he said.
Vemurafenib, the BRAF inhibitor, is “surprisingly” effective in 90% of classic hairy cell leukemia patients with the BRAF V600E mutation, Dr. Allan added, though only about 40% of patients achieve complete response.
In discussing therapy options for a hairy cell leukemia patient previously treated with purine analogues and vemurafenib, Dr. Allan noted that the data behind ibrutinib includes case reports and early clinical investigations.
Several phase 1 studies with small numbers of patients show response rates “in the 50% range,” he said.
“This is an option,” he said. “It’s in the guidelines, and it’s something to consider.”
Moxetumomab pasudotox was recently approved for intravenous use in adults with relapsed or refractory hairy cell leukemia who have had at least two previous systemic treatments, including a purine nucleoside analogue. The CD22-directed cytotoxin is the first of its kind for treating patients with hairy cell leukemia, according to the Food and Drug Administration.
In a single-arm, open-label clinical trial including 80 patients with hairy cell leukemia who had previous treatment in line with that indication, 75% had a partial or complete response, of whom 30% had a durable complete response (CR), defined as maintaining hematologic remission for at least 180 days following CR.
Following the FDA’s approval of moxetumomab pasudotox, the NCCN updated its hairy cell leukemia clinical practice guidelines to include the drug as a category 2A recommendation for relapsed/refractory treatment. Other category 2A options in that setting include ibrutinib, vemurafenib with or without rituximab, or a clinical trial.
Along with that, NCCN guideline authors added a full page on special considerations for use of moxetumomab pasudotox. That includes advice on monitoring for capillary leak syndrome and hemolytic uremic syndrome, along with guidance on capillary leak syndrome grading and management by grade.
Dr. Zelenetz reported financial disclosures related to Adaptive Biotechnology, Amgen, AstraZeneca, Celgene, Genentech, Gilead, Hoffman La Roche, MEI Pharma, MorphoSys AG, Novartis, Pfizer, Pharmacyclics, Roche, and Verastem Oncology. Dr. Allan reported disclosures related to AbbVie, Acerta Pharma, Genentech, Pharmacyclics, Sunesis, and Verastem Oncology.