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A Study of Pacritinib for Reducing Bone Marrow Scarring in Patients with Myelofibrosis Who Have Low Platelet Counts

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What is this trial about?

A plain-language summary of the goals, design and what participants do

This study involves patients with myelofibrosis, a condition affecting the bone marrow where scar tissue builds up and interferes with normal blood cell production. Specifically, the study focuses on patients who also have thrombocytopenia, which means they have low levels of platelets in their blood. Platelets are blood cells that help with clotting and stopping bleeding. The treatment being studied is pacritinib, also known by its code name SB1518, which is given as a hard capsule taken by mouth. This medication works by blocking certain proteins called JAK2 and FLT3 kinases that are involved in the disease process.

The purpose of this study is to evaluate the effect of pacritinib on bone marrow fibrosis, which is the scarring in the bone marrow. The study will examine whether the treatment can reduce the amount of scar tissue in the bone marrow after 52 weeks of treatment. Patients will take pacritinib daily, with a maximum daily dose of 400 milligrams, for up to 24 months. During the study, patients will have regular monitoring that includes bone marrow biopsies, which involve taking a small sample of bone marrow tissue for examination, and MRI scans, which are imaging tests that use magnetic fields to create detailed pictures of the inside of the body.

The study will also look at several other effects of the treatment, including changes in bone marrow fat content measured by MRI, improvements in red blood cell levels and the need for blood transfusions, changes in platelet counts, reduction in spleen size for those with an enlarged spleen, and changes in symptoms related to myelofibrosis. Additionally, the study will monitor genetic changes in the blood, measure various substances in the blood called cytokines, and track any side effects that occur during treatment. Patients will be asked to complete questionnaires about their symptoms throughout the study period.

The research process

The trial runs in 6 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial assessment and baseline measurements

    At the start of the study, a bone marrow biopsy will be performed. This is a procedure where a small sample of bone marrow tissue is taken, usually from the hip bone, to examine the level of scarring in the bone marrow.

    A magnetic resonance imaging scan (also called an MRI scan) will be performed to measure the fat content in the bone marrow.

    Blood samples will be collected to measure hemoglobin levels (the protein in red blood cells that carries oxygen), platelet counts (cells that help blood clot), and genetic markers.

    A splenic volume measurement will be taken if the spleen is enlarged. The spleen is an organ on the left side of the abdomen.

    A questionnaire will be completed to assess symptoms related to the condition.

  2. Step 2

    Starting treatment with pacritinib

    Treatment with pacritinib will begin. This medication is taken by mouth in the form of a capsule.

    The specific dosage, frequency, and duration of taking pacritinib will be determined by the treating physician based on individual medical needs.

    The medication will be taken continuously throughout the study period.

  3. Step 3

    Regular monitoring during the first 24 weeks

    During the first 24 weeks of treatment, regular visits will be scheduled to monitor health status and treatment effects.

    Blood samples will be collected periodically to check hemoglobin levels, platelet counts, and other blood parameters.

    Any need for red blood cell transfusions (a procedure where blood is given through a vein to treat low red blood cell counts) will be tracked.

    Symptoms will be assessed regularly using a questionnaire.

    Any side effects or adverse reactions to the medication will be monitored and recorded.

  4. Step 4

    Assessment at week 24

    At week 24, a bone marrow biopsy will be performed to evaluate changes in bone marrow scarring compared to the start of the study.

    An MRI scan will be performed to measure changes in bone marrow fat content.

    Blood samples will be collected to measure changes in genetic markers, hemoglobin levels, and platelet counts.

    If the spleen was enlarged at the start, a measurement will be taken to assess any changes in splenic volume.

    Blood samples will be taken to measure levels of certain proteins called cytokines that are involved in inflammation and immune responses.

    The bone marrow sample will be analyzed for certain molecular markers related to the disease.

  5. Step 5

    Continued treatment from week 24 to week 52

    Treatment with pacritinib will continue from week 24 through week 52.

    Regular monitoring visits will continue to assess health status, blood counts, and any side effects.

    Symptoms will continue to be assessed using questionnaires.

    Any need for red blood cell transfusions will continue to be tracked.

  6. Step 6

    Final assessment at week 52

    At week 52, a bone marrow biopsy will be performed to evaluate changes in bone marrow scarring compared to the start of the study.

    An MRI scan will be performed to measure changes in bone marrow fat content.

    Blood samples will be collected to measure changes in genetic markers, hemoglobin levels, and platelet counts.

    If the spleen was enlarged at the start, a measurement will be taken to assess any changes in splenic volume.

    Final assessments of treatment effects, side effects, and overall health status will be completed.

Who can join the trial?

17 criteria

  • You must be at least 18 years old
  • You must have a confirmed diagnosis of myelofibrosis, which is a condition affecting the bone marrow. This includes primary myelofibrosis (the condition started on its own) or myelofibrosis that developed after polycythemia vera (a blood disorder with too many red blood cells) or after essential thrombocythemia (a blood disorder with too many platelets)
  • Your platelet count (cells that help blood clot) must be between 50 and 120 x10e9 per liter, which is lower than normal
  • Your doctor must believe you need treatment with a JAK-2 inhibitor (a type of medicine that blocks certain proteins in the body) and you are suitable to start treatment with pacritinib. This can be either as your first treatment with this type of medicine or as a second treatment if a previous JAK-2 inhibitor did not work, stopped working, or caused problems you could not tolerate
  • If you had previous treatment, you must have recovered from any side effects to a mild level or less
  • Your ECOG Performance Status (a measure of how well you can perform daily activities) must be 0, 1, or 2, meaning you are able to care for yourself
  • Your DIPSS score (a scoring system that predicts how the disease may progress) must be Intermediate-1, Intermediate-2, or High risk
  • Your peripheral blast count (immature blood cells in your bloodstream) must be less than 5 percent
  • Your absolute neutrophil count (a type of white blood cell that fights infection) must be at least 500 per microliter
  • Your blood clotting tests, called prothrombin time, international normalized ratio, and partial thromboplastin time, must be no more than 1.5 times the upper normal limit
  • Your liver function must be adequate, meaning your liver enzymes (ALT and AST, which are proteins that indicate liver health) must be no more than 3 times the upper normal limit, or no more than 5 times if the increase is due to myelofibrosis
  • Your bilirubin levels (a substance produced when the liver breaks down old red blood cells) must be no more than 4 times the upper normal limit
  • Your kidney function must be adequate, with an estimated glomerular filtration rate (a measure of how well your kidneys filter waste) greater than 30 milliliters per minute
  • If you are able to have children, you must be willing to use effective birth control during the study and for 30 days after your last dose of the study medicine
  • You must be willing and able to undergo frequent MRI scans (a type of imaging test using magnets) and bone marrow biopsies (a procedure where a small sample of bone marrow is removed for testing)
  • You must be able to understand and willing to complete questionnaires about your symptoms
  • You must sign a written consent form voluntarily agreeing to participate in the study

Who cannot join the trial?

4 criteria

  • The source data does not provide specific exclusion criteria, which are reasons why a patient cannot participate in the study
  • Without detailed exclusion criteria listed in the study information, it is not possible to identify which conditions, medications, or other factors would prevent participation
  • The study is designed for patients with myelofibrosis, which is a rare bone marrow disorder that affects the body's ability to produce blood cells, and who have platelet counts between 50 and 120, where platelets are small blood cells that help with clotting
  • The study accepts both male and female adult and elderly patients
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Investigated drugs

Pacritinib is a medicine being tested in this study to see if it can help reduce scarring (fibrosis) in the bone marrow of patients with myelofibrosis who also have low platelet counts (thrombocytopenia). Myelofibrosis is a condition where the bone marrow becomes scarred and cannot make blood cells properly. This medication is being studied to see if it can improve the condition of the bone marrow in these patients.

What is already known about the treatment

Pacritinib – Pacritinib is an oral medication that belongs to a class of drugs called JAK2 inhibitors, which work by blocking specific proteins in the body that contribute to abnormal blood cell production and bone marrow scarring. This medication is being studied for the treatment of myelofibrosis, a rare bone marrow disorder that causes excessive scar tissue formation and affects normal blood cell production, particularly in patients who have low platelet counts. Pacritinib works at the molecular level by inhibiting Janus kinase 2 (JAK2) enzymes, which are overactive in myelofibrosis and lead to inflammation and progressive scarring of the bone marrow. The medication is currently being evaluated in clinical trials to determine its effectiveness in reducing bone marrow fibrosis in patients with platelet counts between 50 and 120 thousand per microliter of blood.

Investigated diseases

Myelofibrosis – Myelofibrosis is a rare bone marrow disorder that disrupts the body's normal production of blood cells. The disease causes scar tissue to build up inside the bone marrow, where blood cells are normally made. As the scarring increases, the bone marrow becomes less able to produce healthy blood cells. This leads to a shortage of red blood cells, which causes anemia and fatigue, and can also affect white blood cells and platelets. The spleen often becomes enlarged as it tries to take over blood cell production. Over time, the bone marrow becomes increasingly filled with fibrous scar tissue, making it progressively harder for the body to maintain normal blood cell counts.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IITrial ID2025-522509-39-00Protocol codeGEMFIN-MF-PACRI 2401Estimated enrolment30 patientsSponsorGrupo Espanol De Enfermedades Mieloproliferativas Cronicas Ph

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