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Health condition · Clinically reviewed

Myelofibrosis, a rare marrow disorder with a clear, risk-led treatment path.

When scar tissue replaces bone marrow, the spleen steps in - and treatment is matched to risk, from watchful waiting to transplant.

Jump to treatment
A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against NICE, BSH and peer-reviewed haematology sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK guidance including JAK inhibitors, DIPSS scoring and transplant eligibility.

Key facts

Myelofibrosis at a glance.

The essentials, in plain English - what it is, why the spleen enlarges, and how it’s risk-stratified and treated in the UK today.

  • What it is

    A rare myeloproliferative neoplasm - bone marrow is progressively replaced by fibrous scar tissue, impairing blood cell production.

  • Origin

    Can arise on its own (primary myelofibrosis) or evolve from polycythaemia vera or essential thrombocythaemia.

  • Driver mutations

    Most cases carry a JAK2, CALR or MPL mutation - each with a different prognosis and treatment implication.

  • Hallmark sign

    Splenomegaly from extramedullary haematopoiesis - the spleen takes over blood cell production the marrow can no longer manage.

  • Risk scoring

    DIPSS (Dynamic International Prognostic Scoring System) stratifies patients into low, intermediate and high risk to guide treatment.

  • Only cure

    Allogeneic stem cell transplant is the sole curative option - reserved for eligible higher-risk patients.

Why this guide matters

A risk-led plan, not a one-size approach.

Myelofibrosis is rare, varies enormously in pace, and - with the right risk stratification - is managed with a plan matched to you. The three points below shape everything else on this page.

  • Not every case needs treatment now

    Asymptomatic low-risk disease is often watched closely rather than treated - overtreatment carries its own risks.

  • JAK inhibitors changed the landscape

    Ruxolitinib and newer agents control spleen size and symptoms for many, transforming day-to-day quality of life.

  • Transplant is curative, but selective

    Allogeneic stem cell transplant can cure myelofibrosis, but eligibility depends on age, fitness and risk - an early conversation keeps the door open.

How the diagnosis is made

From an odd blood film to a clear plan.

The steps a UK haematology team will normally follow, in order - so you know what to expect and why.

  1. 01

    Assessing

    FBC and blood film

    A leucoerythroblastic picture with teardrop-shaped red cells (dacrocytes) is the classic clue that points towards marrow fibrosis.

  2. 02

    Assessing

    Clinical assessment

    Fatigue, night sweats, weight loss, abdominal discomfort and bone pain are reviewed alongside a careful examination for splenomegaly.

  3. 03

    Confirming

    Bone marrow biopsy

    The definitive test - a trephine biopsy grades the degree of reticulin or collagen fibrosis and confirms the diagnosis.

  4. 04

    Confirming

    JAK2, CALR and MPL testing

    Molecular testing identifies the driver mutation, informing both prognosis and eligibility for targeted therapy.

  5. 05

    Confirming

    Imaging for spleen size

    Ultrasound or CT measures splenomegaly objectively and provides a baseline to track response to treatment.

  6. 06

    Preparing

    DIPSS risk stratification

    Age, haemoglobin, white cell count, blast percentage and constitutional symptoms combine into a risk score that shapes the treatment plan.

  7. 07

    Preparing

    Specialist haematology referral

    Myelofibrosis is managed in specialist commissioned haematology services, often with an MDT reviewing transplant eligibility.

Typical timeline: an abnormal blood film to a risk-stratified plan in a few weeks.

Symptoms

What myelofibrosis actually feels like.

Many symptoms come from anaemia and an enlarging spleen. And the features that mean it’s time to seek urgent review.

  • Fatigue

    Often the earliest and most persistent symptom - driven by anaemia and the metabolic burden of the disease.

  • Night sweats

    Drenching sweats are a constitutional symptom that feeds into the DIPSS risk score.

  • Unintentional weight loss

    A hypermetabolic state can cause steady weight loss without any change in diet.

  • Early satiety and abdominal discomfort

    A grossly enlarged spleen presses on the stomach, causing fullness after small meals and left-sided discomfort.

  • Bone pain

    Aching in the long bones can reflect marrow fibrosis and the pressure of expanding haematopoietic tissue.

  • Bruising and bleeding

    Low or dysfunctional platelets can cause easy bruising, gum bleeding or prolonged bleeding after minor injury.

  • Symptoms of anaemia

    Breathlessness, pallor and light-headedness reflect the marrow’s failing ability to produce red cells.

  • Red flag - rapidly enlarging spleen

    A spleen that is growing quickly or causing severe pain needs urgent haematology assessment.

Treatment

How myelofibrosis is treated in the UK.

Watchful waiting for low-risk disease, JAK inhibitors and supportive care for symptomatic disease - and transplant for eligible higher-risk patients.

  • Watchful waiting

    Appropriate for asymptomatic low-risk disease - regular monitoring without active treatment while the condition remains stable.

  • Ruxolitinib (JAK inhibitor)

    Reduces spleen size and constitutional symptoms in intermediate and high-risk disease - the mainstay of medical therapy.

  • Newer JAK inhibitors

    Fedratinib and momelotinib offer alternatives, the latter also addressing anaemia associated with myelofibrosis.

  • Blood transfusions

    Supportive care for symptomatic anaemia, used alongside other measures to maintain quality of life.

  • Growth factors

    Erythropoiesis-stimulating agents can help selected patients with anaemia who are not transfusion-dependent.

  • Splenic radiotherapy

    Low-dose radiotherapy can shrink a symptomatic spleen when medical treatment has not been enough, though benefit is often temporary.

  • Splenectomy

    Surgical removal considered for refractory, severely symptomatic splenomegaly - a significant operation reserved for carefully selected patients.

  • Allogeneic stem cell transplant

    The only potentially curative option - offered to eligible higher-risk patients through an MDT specialist commissioned pathway.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist haematology society standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your haematology team knows your disease and history and can tell you which parts apply to you. If in doubt, get seen.

  • British Society for Haematology (BSH). Guideline for the diagnosis and management of myelofibrosis.

  • NICE. Ruxolitinib for treating disease-related splenomegaly or symptoms in myelofibrosis (TA386).

  • European LeukemiaNet. Recommendations for the management of myeloproliferative neoplasms.

  • NHS England. Specialised commissioning for haematological cancers - stem cell transplantation.

Red flags

When myelofibrosis needs urgent attention.

Most disease is monitored in specialist clinics on a planned schedule. These are the situations that need faster review.

  • Rapidly enlarging spleen

    Fast growth or severe left upper quadrant pain warrants urgent haematology review to exclude splenic infarction or rupture risk.

  • Blast phase transformation

    Progression to acute myeloid leukaemia is the most feared complication - a sudden rise in blast cells needs immediate specialist input.

  • Severe anaemia or transfusion dependence

    A steep drop in haemoglobin or new transfusion need signals disease progression and should prompt urgent review.

  • Significant bleeding

    Spontaneous bruising, mucosal bleeding or bleeding that will not stop reflects thrombocytopenia or platelet dysfunction needing urgent assessment.

  • New or worsening bone pain

    Severe, persistent bone pain deserves imaging and specialist review to assess disease extent.

  • Splenic infarction

    Sudden severe abdominal pain with fever can indicate infarction of an enlarged spleen - an emergency presentation.

  • Portal hypertension

    Extramedullary haematopoiesis can involve the liver, occasionally causing portal hypertension and its complications.

  • Constitutional symptom escalation

    Worsening night sweats, weight loss or fevers can indicate disease progression and should trigger DIPSS reassessment.

Living with it

A rare condition, with a clear monitoring rhythm.

Four things that make the biggest difference day to day - steady monitoring, pacing energy, prompt reporting of new symptoms and planning ahead on transplant.

A quiet reminder

Disease pace varies enormously - your plan is personal.

Some people live for years with stable, low-risk disease. Others need earlier, more active treatment. Your DIPSS score and symptoms guide the pace, not a generic timeline.

  1. 01 Monitor

    Keep review appointments

    Regular blood counts and clinical review track disease pace and catch progression early, even when you feel well.

  2. 02 Energy

    Pace fatigue, don’t fight it

    Fatigue from anaemia is real, not laziness - build rest into the day and prioritise what matters most.

  3. 03 Symptoms

    Report new symptoms promptly

    New bone pain, bruising, fevers or rapid abdominal swelling should be flagged to your haematology team without delay.

  4. 04 Plan

    Discuss transplant early

    For higher-risk disease, an early conversation about stem cell transplant eligibility keeps options open while you are fit for it.

Frequently asked

Everything we get asked about myelofibrosis.

Quick answers on causes, the spleen, JAK inhibitors and transplant.

  • What is myelofibrosis?

    A rare myeloproliferative neoplasm in which bone marrow is progressively replaced by fibrous scar tissue, impairing normal blood cell production. The body compensates through extramedullary haematopoiesis, typically in the spleen, which becomes enlarged.

  • Is myelofibrosis the same as leukaemia?

    No, though it belongs to the same family of blood disorders and can transform into acute myeloid leukaemia in a minority of cases. Myelofibrosis itself is classed as a myeloproliferative neoplasm, not a leukaemia.

  • What causes myelofibrosis?

    Most cases are driven by a JAK2, CALR or MPL gene mutation that causes bone marrow cells to overproduce, triggering fibrosis. It can develop on its own or evolve from polycythaemia vera or essential thrombocythaemia.

  • Why does the spleen get so large?

    When the marrow can no longer make enough blood cells, the spleen (and sometimes the liver) takes over some of that work - a process called extramedullary haematopoiesis. This causes the spleen to enlarge, sometimes substantially.

  • What does ruxolitinib do?

    It is a JAK inhibitor that blocks the overactive signalling driving the disease, reducing spleen size and easing constitutional symptoms such as night sweats and fatigue. It does not cure myelofibrosis but improves quality of life for many patients.

  • Is myelofibrosis curable?

    The only potentially curative treatment is allogeneic stem cell transplant, which is offered to eligible higher-risk patients after careful MDT assessment. For others, treatment focuses on controlling symptoms and monitoring disease pace.

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