Limited treatment options for cytopenic myelofibrosis patients have existed until very recently, leaving a gap in care for individuals combating the often debilitating condition. The overall incidence of myelofibrosis is estimated at 1.5 cases/100,000 people in the US, and approximately two-thirds of those with the disease have cytopenias (either anemia or thrombocytopenia). A new treatment option that does not further lower platelet counts may be groundbreaking for those with life-threatening thrombocytopenia.

The cause of primary myelofibrosis is unknown, as it is a complex disease with multiple factors involved in its development. Its rarity contributes to the incomplete nature of researchers' understanding of the condition, and continued study will be ongoing. The blood cancer is known for the scar tissue or fibrosis that develops in bone marrow. Sometimes myelofibrosis is found during common blood testing of patients, with the individual not yet aware of the illness. As the fibrosis escalates, blood cell production is affected. Symptoms will emerge, including fatigue, weakness, pale skin (low red blood cells), frequent infections (low white blood cells), frequent bruising or bleeding (low platelets), splenomegaly, hepatomegaly, pruritus, pyrexia, weight loss, and bone or joint pain.

Treatment of myelofibrosis focuses on the specific symptoms that a particular patient experiences. A person may remain asymptomatic for a long while; therefore, pharmacotherapy may be reserved until disease progression. Depending on the course the disease takes, treatments may include medications and blood transfusions, chemotherapy, splenectomy, or bone marrow transplant. Until recently, the pharmacological approvals for myelofibrosis treatment have included Jakafi (ruxolitinib) and Inrebic (fedratinib). These medications are appropriate for patients with platelet counts of ≥50,000/µL. Unfortunately, they are capable of causing anemia or fewer platelets. For these situations, the recent approval of Vonjo (pacritinib) can be a great benefit. Pacritinib has shown that it does not further lower platelet counts while still improving splenomegaly and its symptoms. Its specific indication is for the treatment of adults with intermediate or high-risk primary or secondary (post-polycythemia vera or post-essential thrombocythemia) myelofibrosis with a platelet count below 50×10⁹ /L. It is supplied as 100mg capsules in 120-count bottles. Pacritinib is an oral kinase inhibitor with specificity for JAK2 and IRAK1, without inhibiting JAK1.

Researchers believe that the success of pacritinib is related to its ability to target other cellular signals than ruxolitinib and fedratinib are able to. The drug's performance was demonstrated in the Phase 3 PERSIST-2 study. Patients who met the appropriate criteria for the study were randomized 1:1:1 to receive pacritinib 200mg twice daily, 400mg once daily, or best available therapy. The study concluded that 29% of those treated with pacritinib 200mg twice daily had a reduction in spleen volume of at least 35% compared to 3% of patients receiving best available therapy. The efficacy results helped pacritinib achieve an accelerated FDA approval. A confirmatory trial, PACIFICA, is underway as part of the post-approval plans and results are expected within 2025.

No current drug therapy can cure myelofibrosis. For now, treatment remains focused on controlling symptoms and resulting complications, improving quality of life and extending survival. Groundbreaking advancements like the introduction of pacritinib as a therapeutic option help fill a significant gap in treating cytopenic myelofibrosis. Stay informed about drug information, including medications for treating myelofibrosis, by updating or registering your profile to receive email alerts and other critical drug information updates from PDR. You can also stay current by using the official PDR app, mobilePDR, available for free from your favorite app stores