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# Acute promyelocytic leukaemia

- Lesion

A leukaemia that bleeds: abnormal promyelocytes trigger clotting and fibrinolysis, but a vitamin A drug makes them mature and most patients are cured.

Updated Nov 12, 2026

## Key points

- t(15;17) PML::RARA; the fusion represses genes needed for granulocytic differentiation.
- Abnormal promyelocytes with dense granules and bundles of Auer rods (faggot cells).
- DIC with marked hyperfibrinolysis at presentation: a medical emergency.
- All-trans retinoic acid (a vitamin A derivative) plus arsenic trioxide cure more than 90% of patients.
- Differentiation syndrome can follow treatment: fever, lung infiltrates and fluid retention.

On this page

- The basics Key points
- What it is
- Structure
- Step by step
- Markers
- Memory aid
- Elsewhere in DurgiPedia

- Clinical Clinical notes
- In the lab

- Study Test yourself

- Connections Connections

## What it is

Acute promyelocytic leukaemia (APL) is the AML defined by t(15;17), which fuses PML to the retinoic acid receptor alpha (RARA). The fusion protein blocks maturation at the promyelocyte stage. The granules of these cells release procoagulants and fibrinolytic activators, so patients present with disseminated intravascular coagulation and a high risk of early fatal haemorrhage. Pharmacologic doses of all-trans retinoic acid and arsenic trioxide overcome the block, and APL has become the most curable AML.

## Structure

- Marrow replaced by promyelocytes with heavy azurophilic granulation and bilobed or kidney-shaped nuclei.
- Faggot cells: promyelocytes packed with many Auer rods.
- A microgranular variant has few visible granules and a high white count.

## Step by step

- t(15;17) creates the PML::RARA fusion protein.
- The fusion binds retinoic acid response elements and recruits corepressors, freezing cells at the promyelocyte stage.
- Promyelocytes accumulate; their granules expose tissue factor and annexin II and activate plasminogen.
- Clotting and fibrinolysis both run: DIC with severe bleeding.
- Retinoic acid at high levels releases the repression; arsenic degrades the fusion protein; cells mature and die.

## Markers

- MPO strongly positive
- CD33
- CD13
- CD34 and HLA-DR usually negative

## Clinical notes

- Bleeding gums, extensive bruising and intracranial haemorrhage in a patient with pancytopenia.
- Treatment starts on suspicion, before genetic confirmation, because early haemorrhagic death is the main threat.

## In the lab

- Low fibrinogen, prolonged PT, high D-dimer, thrombocytopenia.
- FISH or PCR for PML::RARA confirms the diagnosis.

## Memory aid

Fifteen seventeen, faggots and fibrinolysis: give vitamin A's cousin and the promyelocytes grow up.

## Test yourself

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

## Which fusion gene defines APL?

PML::RARA, from t(15;17).

## Why do patients with APL bleed?

Promyelocyte granules release procoagulants and fibrinolytic activators, producing DIC with hyperfibrinolysis.

## How does all-trans retinoic acid work in APL?

At high levels it overcomes the repression by the PML::RARA protein so the promyelocytes differentiate.

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## Elsewhere in DurgiPedia

- [Vitamin A (retinol)](https://durgical.com/en/biochemistry/molecules/vitamin-a/)

## Connections

## Related 4

- [Disseminated intravascular coagulation: how consumption causes both clots and bleeding](https://durgical.com/en/general-pathology/disseminated-intravascular-coagulation-how-consumption-causes-both-clots-and-ble/)
- [Acute myeloid leukaemia](https://durgical.com/en/general-pathology/acute-myeloid-leukaemia/)
- [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/)
- [Bleeding disorders: overview](https://durgical.com/en/general-pathology/bleeding-disorders-overview/)

## Related conditions 2

- [Acute leukaemia (AML and ALL)](https://durgical.com/en/conditions/acute-leukaemia/)
- [Disseminated intravascular coagulation](https://durgical.com/en/conditions/disseminated-intravascular-coagulation/)

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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: [Acute promyelocytic leukemia: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/acute-promyelocytic-leukemia/) (MedlinePlus, US National Library of Medicine, 2026); [Acute Myeloid Leukemia Treatment (PDQ®)–Patient Version](https://www.cancer.gov/types/leukemia/patient/adult-aml-treatment-pdq) (National Cancer Institute (NCI), 2026).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/acute-promyelocytic-leukaemia/