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A Phase 3 Study of Sapablursen Compared with Placebo in Adults with Polycythemia Vera

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What is this trial about?

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

The study focuses on Polycythemia Vera, a rare blood condition where the body makes too many red blood cells, causing the blood to become thicker than normal. The investigational medication being tested is called Sapablursen, which is given as a subcutaneous injection (a small needle placed under the skin). A matching placebo that looks the same but does not contain the active drug is also used. The purpose of the study is to compare how well Sapablursen works against the placebo in controlling the disease over a period of about eight months.

Participants are randomly assigned to receive either Sapablursen or the placebo, and neither the participants nor the study staff know which treatment is given (double‑blind). Throughout the study, regular blood tests are performed to measure the hematocrit level (the proportion of red blood cells in the blood). If the hematocrit rises above a certain level, a phlebotomy—a simple procedure where a small amount of blood is drawn to lower the count—may be needed. Researchers also ask participants to complete short questionnaires about fatigue and other symptoms to see how the treatment affects daily feeling. The trial lasts roughly 32 weeks, with visits scheduled at regular intervals to monitor safety, any side effects, and overall health.

The research process

The trial runs in 7 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial study visit and randomization

    You attend the first clinic appointment after joining the study. during this visit baseline blood tests are taken and your medical information is recorded. you are randomly assigned to receive either Sapablursen or a matching placebo. the assigned product is prepared as a subcutaneous injection (injection under the skin) in a solution for injection.

    The injection contains a concentration of 0 mg/ml as described in the product information. the exact schedule for receiving the injection is defined by the study protocol and will be followed at each subsequent clinic visit.

  2. Step 2

    Regular study medication administration

    You receive the assigned injection at each scheduled clinic visit. the injection is given under the skin (subcutaneous). the dose remains the same throughout the period you are on study treatment.

    The treatment period lasts for at least 32 weeks for all participants. participants who continue in the extended phase may receive the medication for up to 52 weeks.

  3. Step 3

    Routine blood testing for hematocrit monitoring

    At every clinic visit you provide a blood sample that is used to measure hematocrit (Hct), the proportion of red blood cells in the blood. these measurements are taken from week 0 through week 32, and for some participants also through week 52.

    The study aims to keep Hct values below 45 % without the need for phlebotomy. a single Hct value of 45 % or higher is allowed, but higher values may trigger additional actions.

  4. Step 4

    Assessment of phlebotomy need

    Based on the Hct results, the study team determines whether you meet criteria for phlebotomy (removal of blood to lower Hct). criteria include Hct ≥45 % that is at least 3 % above the baseline on two consecutive tests, or Hct ≥48 %. if criteria are met, phlebotomy may be performed according to the study rules.

  5. Step 5

    Patient‑reported outcomes questionnaire

    At week 32 you complete questionnaires that assess fatigue and other symptoms. the tools used are the PROMIS Fatigue Short Form 8a and the Myelofibrosis Symptom Assessment Form version 4.0. your responses are recorded to evaluate how the study medication affects quality of life.

  6. Step 6

    Safety monitoring and reporting

    Throughout the study you are asked to report any new symptoms, side effects, or health changes. regular laboratory tests are performed to identify any treatment‑emergent adverse events. if serious problems occur, the study medication may be reduced, paused, or stopped according to safety guidelines.

  7. Step 7

    Final study assessments and treatment discontinuation

    At the end of the primary 32‑week period (or at week 52 for the extended follow‑up) you attend a final clinic visit. final blood tests, safety evaluations, and outcome assessments are completed. the study medication is discontinued, and you receive information about any further medical care that may be needed.

Who can join the trial?

7 criteria

  • You must sign a written informed consent form, meaning you understand the study and can follow its rules.
  • You need to have a confirmed diagnosis of Polycythemia Vera that meets the 2022 World Health Organization (WHO) and International Consensus Classification (ICC) guidelines (these are official ways doctors identify the disease).
  • You must be phlebotomy‑dependent, which means you regularly need blood removal to keep your condition under control.
  • Your hematocrit level (the percentage of red blood cells in your blood) must be less than 45% when the study starts.
  • You must have adequate organ function and normal electrolytes (the chemicals in your body that help muscles and nerves work properly).
  • If you are taking cytoreduction therapy (CRT) (medication that lowers blood cell production), your dose must be stable and unchanged at the beginning of the study.
  • Both men and women are eligible to participate.

Who cannot join the trial?

6 criteria

  • You have already been treated for Polycythemia Vera with medicines that block a protein called TMPRSS6 (such as sapablursen or drugs that act like the natural hormone hepcidin); this means you cannot join the study.
  • You had a serious blood clot (called thrombosis) such as a heart attack, stroke, deep vein clot, or clot in the spleen’s vein within the month before the study starts.
  • You need regular blood removal (called phlebotomy) because your blood’s hematocrit level is below 45%, which makes you ineligible.
  • You meet the medical definition of post‑PV myelofibrosis, a condition where scar tissue forms in the bone marrow after Polycythemia Vera.
  • You have any serious, unstable medical problem or an uncontrolled mental health (psychiatric) condition that the doctor thinks would prevent you from following the study rules.
  • If you are a woman who is currently pregnant, planning to become pregnant during the study, or breastfeeding, you cannot take part.
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Investigated drugs

Sapablursen is an experimental drug being tested in this study for people with polycythemia vera, a condition where the blood makes too many red cells. It is given as a liquid that is injected just under the skin (subcutaneous injection). The purpose of the drug in the trial is to see if it can reduce the number of red blood cells and improve symptoms compared with no active treatment.

What is already known about the treatment

Sapablursen - Sapablursen is supplied as a clear solution for subcutaneous injection, meaning it is given under the skin with a small needle. It is still an investigational drug and is currently in Phase 3 clinical trials, so it has not yet received regulatory approval. The medicine is being tested for use in polycythemia vera, a condition where the bone marrow makes too many red blood cells. It works by blocking a specific protein that tells the marrow to produce blood cells and is classified as a targeted JAK2‑inhibitor therapy.

Investigated diseases

Polycythemia vera - Polycythemia vera is a blood disorder in which the bone marrow produces too many red blood cells. The excess cells make the blood thicker, which can cause the spleen to enlarge and may increase overall blood volume. Over time, the condition can also raise the numbers of white blood cells and platelets. As the disease advances, the bone marrow may become scarred, leading to changes in the production of other blood cells.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2025-524669-25-00Protocol codeONO-0530-03-001Estimated enrolment261 patientsSponsorDeciphera Pharmaceuticals Inc.

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