Durgical
EN
Open the app

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

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

  1. t(15;17) creates the PML::RARA fusion protein.
  2. The fusion binds retinoic acid response elements and recruits corepressors, freezing cells at the promyelocyte stage.
  3. Promyelocytes accumulate; their granules expose tissue factor and annexin II and activate plasminogen.
  4. Clotting and fibrinolysis both run: DIC with severe bleeding.
  5. 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.

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.

Add to my cards (3)

More Pathology questions →

Elsewhere in DurgiPedia

Connections

← All of 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: Acute promyelocytic leukemia: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Acute Myeloid Leukemia Treatment (PDQ®)–Patient Version (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.