[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [White cells, lymph nodes, spleen and thymus](https://durgical.com/en/general-pathology/areas/hematolymphoid/) › Myeloproliferative neoplasms: overview

# Myeloproliferative neoplasms: overview

- Topic

Marrow stem cells with a stuck-on growth signal make too many mature blood cells. Later the marrow can scar or turn to leukaemia.

Updated Nov 12, 2026

## Key points

- BCR::ABL1 defines CML; JAK2 V617F is present in nearly all PV and about half of ET and PMF.
- CALR or MPL mutations account for most JAK2-negative ET and PMF; mutant CALR activates the thrombopoietin receptor.
- Shared features: hypercellular marrow, splenomegaly from extramedullary haematopoiesis, spent phase with fibrosis, risk of AML.
- Thrombosis (including Budd–Chiari and portal vein) and bleeding from abnormal platelets.
- Systemic mastocytosis (KIT D816V) is grouped with the myeloid neoplasms.

## What it is

Myeloproliferative neoplasms (MPNs) are clonal stem cell disorders driven by constitutively active tyrosine kinase signalling. Unlike MDS, maturation is effective, so blood counts are high. The main entities are chronic myeloid leukaemia (BCR::ABL1), polycythaemia vera, essential thrombocythaemia and primary myelofibrosis (JAK2, CALR or MPL mutations). All tend to colonize spleen and liver (extramedullary haematopoiesis), cause thrombosis or bleeding, burn out into marrow fibrosis (the spent phase) or transform to acute leukaemia.

## Step by step

- A stem cell acquires a kinase-activating mutation (BCR::ABL1, JAK2, CALR or MPL).
- Growth factor-independent signalling (JAK–STAT, RAS–MAPK) drives production of mature cells.
- Blood counts rise: granulocytes in CML, red cells in PV, platelets in ET.
- Neoplastic stem cells home to spleen and liver: extramedullary haematopoiesis, splenomegaly.
- Over years, megakaryocyte cytokines (PDGF, TGF-β) scar the marrow (spent phase), or new mutations cause blast transformation.

## The four classic myeloproliferative neoplasms

| Neoplasm | Driver | Main blood finding | Marrow | Main complication |
| --- | --- | --- | --- | --- |
| [Chronic myeloid leukaemia](https://durgical.com/en/conditions/chronic-myeloid-leukaemia/) | BCR::ABL1, t(9;22) | Neutrophilia with all stages, basophilia | Hypercellular, granulocytes and small megakaryocytes | Blast crisis |
| [Polycythaemia vera](https://durgical.com/en/conditions/polycythaemia-vera/) | JAK2 V617F (exon 12 in a few) | High red cell mass, often also platelets and neutrophils; low EPO | Panmyelosis | Thrombosis, spent phase |
| [Essential thrombocythaemia](https://durgical.com/en/conditions/essential-thrombocythaemia-and-primary-myelofibrosis/) | JAK2, CALR or MPL | High platelet count | Clusters of giant megakaryocytes | Thrombosis, bleeding, erythromelalgia |
| [Primary myelofibrosis](https://durgical.com/en/conditions/essential-thrombocythaemia-and-primary-myelofibrosis/) | JAK2, CALR or MPL | Anaemia, teardrop cells, leukoerythroblastosis | Fibrosis, atypical megakaryocytes, osteosclerosis | Marrow failure, massive spleen, AML |

## Markers

- BCR::ABL1
- JAK2 V617F
- CALR
- MPL
- Reticulin stain

## Clinical notes

- Unexplained splanchnic vein thrombosis should prompt testing for JAK2 V617F.
- Hyperuricaemia and gout reflect high cell turnover.
- Kinase inhibitors target BCR::ABL1 in CML and JAK2 signalling in myelofibrosis.

## Memory aid

Too much of a good thing: CML too many granulocytes, PV too many red cells, ET too many platelets, PMF too much scar.

## Test yourself

Think of the answer, then tap the question to see it.

## What separates MPNs from MDS?

In MPNs differentiation is effective and blood counts are high; in MDS it is ineffective and counts are low.

## Which mutation is present in nearly all polycythaemia vera?

JAK2 V617F (a few cases have JAK2 exon 12 mutations).

## What is the spent phase of an MPN?

Late marrow fibrosis with falling counts and massive extramedullary haematopoiesis in the spleen.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/myeloproliferative-neoplasms-overview/)

[More Pathology questions →](https://durgical.com/en/practice/?f=pathology)

## Elsewhere in DurgiPedia

- [Hematopoiesis](https://durgical.com/en/physiology/hematopoiesis/)

## Connections

## Related 5

- [Chronic myeloid leukaemia](https://durgical.com/en/general-pathology/chronic-myeloid-leukaemia/)
- [Polycythaemia and polycythaemia vera](https://durgical.com/en/general-pathology/polycythaemia-and-polycythaemia-vera/)
- [Essential thrombocythaemia and primary myelofibrosis](https://durgical.com/en/general-pathology/essential-thrombocythaemia-and-primary-myelofibrosis/)
- [Myelodysplastic neoplasms](https://durgical.com/en/general-pathology/myelodysplastic-neoplasms/)
- [Oncogenes: RAS, MYC, HER2, BCR-ABL and the table to know](https://durgical.com/en/general-pathology/oncogenes-ras-myc-her2-bcr-abl-and-the-table-to-know/)

## Related conditions 6

- [Chronic myeloid leukaemia](https://durgical.com/en/conditions/chronic-myeloid-leukaemia/)
- [Polycythaemia vera](https://durgical.com/en/conditions/polycythaemia-vera/)
- [Essential thrombocythaemia and primary myelofibrosis](https://durgical.com/en/conditions/essential-thrombocythaemia-and-primary-myelofibrosis/)
- [Mastocytosis (cutaneous and systemic)](https://durgical.com/en/conditions/mastocytosis/)
- [Hypereosinophilic syndrome](https://durgical.com/en/conditions/hypereosinophilic-syndrome/)
- [Portal vein thrombosis](https://durgical.com/en/conditions/portal-vein-thrombosis/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Myeloproliferative Neoplasms Treatment (PDQ®)–Patient Version](https://www.cancer.gov/types/myeloproliferative/patient/chronic-treatment-pdq) (National Cancer Institute (NCI), 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/general-pathology/myeloproliferative-neoplasms-overview/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/myeloproliferative-neoplasms-overview/