Conference Coverage

Using JAK inhibitors for myelofibrosis



Despite a growing list of Janus kinase (JAK) inhibitors, ruxolitinib remains the go-to for patients with symptomatic, higher risk myelofibrosis, according to Anthony M. Hunter, MD, a myeloid malignancies specialist at Emory University, Atlanta.

“We are thankfully starting to be blessed with more options than we’ve ever had,” he said, but “in the front-line proliferative setting, ruxolitinib has remained the standard of care.” It’s “well established in higher-risk patients and very much an option for very symptomatic lower-risk patients.”

Dr. Hunter helped his colleagues navigate the evolving field of JAK inhibition for myelofibrosis in a presentation titled “Choosing and Properly Using a JAK Inhibitor in Myelofibrosis,”at the Society of Hematologic Oncology annual meeting.

Ruxolitinib was the first JAK inhibitor for myelofibrosis on the U.S. market, approved in 2011. Two more have followed, fedratinib in 2019 and pacritinib in 2022.

A fourth JAK inhibitor for myelofibrosis, momelotinib, is under Food and Drug Administration review with a decision expected shortly.

JAK inhibitors disrupt a key pathogenic pathway in myelofibrosis and are a mainstay of treatment, but Dr. Hunter noted that they should not replace allogeneic transplants in patients who are candidates because transplants remain “the best way to achieve long term survival, especially in higher risk patients.”

He noted that not every patient needs a JAK inhibitor, especially “lower-risk, more asymptomatic patients who are predominantly manifesting with cytopenias. [They] are less likely to benefit.”

Dr. Hunter said that although ruxolitinib remains a treatment of choice, fedratinib “is certainly an option” with comparable rates of symptom control and splenomegaly reduction. Also, while ruxolitinib is dosed according to platelet levels, fedratinib allows for full dosing down to a platelet count of 50 x 109/L.

“But there’s more GI toxicity than with ruxolitinib, especially in the first couple of months,” he said, as well as a black box warning of Wernicke’s encephalopathy. “I generally put all my [fedratinib] patients on thiamine repletion as a precaution.”

One of the most challenging aspects of using JAK inhibitors for myelofibrosis is their tendency to cause cytopenia, particularly anemia and thrombocytopenia, which, ironically, are also hallmarks of myelofibrosis itself.

Although there’s an alternative low-dose ruxolitinib regimen that can be effective in anemic settings, the approval of pacritinib and most likely momelotinib is particularly helpful for cytopenic patients, “a population which historically has been very hard to treat with our prior agents,” Dr. Hunter said.

Pacritinib is approved specifically for patients with platelet counts below 50 x 109/L; momelotinib also included lower platelet counts in several studies. Both agents indirectly boost erythropoiesis with subsequent amelioration of anemia.

“Momelotinib is an important emerging agent for these more anemic patients,” with a spleen response comparable to ruxolitinib and significantly higher rates of transfusion independence, but with lower rates of symptom control, Dr. Hunter said.

Pacritinib “really helps extend the benefit of JAK inhibitors to a group of thrombocytopenic patients who have been hard to treat with ruxolitinib,” with the added potential of improving anemia, although, like fedratinib, it has more GI toxicity, he said.

There are multiple add-on options for JAK inhibitor patients with anemia, including luspatercept, an erythropoiesis-stimulating agent approved for anemia in patients with myelodysplastic syndromes; promising results were reported recently for myelofibrosis.

Fedratinib, pacritinib, and momelotinib all have activity in the second line after ruxolitinib failure, Dr. Hunter noted, but he cautioned that ruxolitinib must be tapered over a few weeks, not stopped abruptly, to avoid withdrawal symptoms. Some clinicians overlap JAK inhibitors a day or two to avoid issues.

“Clinical trials should still be considered in many of these settings,” he said, adding that emerging agents are under development, including multiple combination therapies, often with JAK inhibitors as the background.

No disclosure information was reported.

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