Skip to main content

FDA Approves New Drug for Patients with Rare Blood Cancer (Myelofibrosis)

Rye Brook, N.Y., February 28, 2022 – The Food and Drug Administration (FDA) recently approved a drug for the treatment of intermediate or high-risk primary or secondary myelofibrosis, the first specifically for patients with severely low platelet counts (thrombocytopenia). 

The FDA approval of pacritinib (Vonjo), an oral kinase inhibitor with specificity for JAK2, IRAK1 and CSF1R, meets an unmet medical need, as approximately one-third of myelofibrosis patients develop severe thrombocytopenia. Pacritinib is particularly important since ruxolitinib and fedratinib, other JAK2 inhibitors approved for use at a full or modified doses for MF, can lower platelet counts and therefore is not recommended for MF patients with severely low platelet counts.

Myelofibrosis (MF) is a rare cancer in a related group of blood cancers known as “myeloproliferative neoplasms” (MPNs), in which bone marrow cells that produce blood cells develop and function abnormally. MF is characterized by the buildup of scar tissue, called fibrosis, and as it increases, the bone marrow cannot make enough healthy blood cells. 

LLS currently has 15 active grants that have a major focus on MPN, representing a $10 million commitment over the next three to five years. Our long-term research has led to critical contributions to our understanding of MPNs over the last two decades including:

  • Uncovering JAK2 Inhibitors: The JAK2 V617F mutation critical for and specific to MPNs was identified by several groups in 2005, including LLS grantee Gary Gilliland, MD, PhD, at the Fred Hutch Cancer Center. In 2008, his lab first reported the evidence of efficacy in mouse models of MPN for fedratinib, a JAK2 inhibitor approved by the FDA in 2019.
  • Studying BET Inhibitors: LLS’s strategic venture philanthropy initiative, Therapy Acceleration Program (TAP), partnered with Constellation Pharmaceuticals in 2012 with a $7.5 million commitment to develop pelabresib, a BET inhibitor, in early-phase clinical trials and was instrumental in the transition to explore this drug in patients with myelofibrosis. Promising clinical data usually associated with JAK inhibitor therapy has been demonstrated.

The approval of pacritinib was supported by data from the PERSIST-2 trial, in which patients were administered pacritinib or the best available therapy (BAT). Patients who received 200 mg pacritinib twice daily demonstrated a higher percentage (29%) of reduction in spleen volume of at least 30 percent compared to patients on the BAT (3%). Further, 23% of patients had a reduction in total symptom scores of at least 50% compared to 13% among patients administered BAT.

As part of the accelerated approval, the drug developer will be expected to demonstrate confirmatory findings of pacritinib in the PACIFICA trial, which is expected to have results in the middle of 2025. The most common adverse reactions following pacritnib twice daily were diarrhea, thrombocytopenia, nausea, anemia and peripheral edema. 

For more information about MPN research funded by LLS, click here.