# Blasts (leukaemic blast cells)

Source: https://onco.cc/terms/blasts/  
OnCo record `blasts` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Immature blood cells that should mature in the marrow but in acute leukaemia multiply without growing up. The percentage of blasts in the marrow defines the disease: 20% or more is acute leukaemia.

## Summary

Normal marrow has under 5% blasts; MDS with excess blasts has 5-19%; AML or ALL is diagnosed at ≥20% (or with defining genetic lesions at lower counts under WHO 2022/ICC). Blasts crowd out normal blood production, causing anaemia, infection and bleeding, and very high counts (hyperleukocytosis) can clog vessels. Remission is defined as under 5% marrow blasts with recovered counts, though flow cytometry and molecular MRD now detect disease far below that. In CML, progression from chronic phase to blast crisis (≥20% blasts) transforms a controllable disease into an acute leukaemia.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: blast count; blast percentage; leukaemic blasts; leukemic blasts; myeloblasts; lymphoblasts; blast crisis; blast phase; excess blasts; circulating blasts

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Blast_cell
- Wikipedia: https://en.wikipedia.org/wiki/Blast_cell

## Connected records

- terms: [Complete response (CR) and partial response (PR)](https://onco.cc/terms/complete-response-term/), [DIPSS, DIPSS-plus and MIPSS70 (myelofibrosis risk scores)](https://onco.cc/terms/dipss-mipss70/), [Flow cytometry (immunophenotyping)](https://onco.cc/terms/flow-cytometry/), [IPSS-R and IPSS-M (myelodysplastic syndrome risk scores)](https://onco.cc/terms/ipss-m-ipss-r/), [Philadelphia chromosome (Ph+, BCR::ABL1)](https://onco.cc/terms/philadelphia-chromosome/), [Sokal and ELTS risk scores (chronic myeloid leukaemia)](https://onco.cc/terms/sokal-elts-scores/)
- cancers: [Acute lymphoblastic leukaemia](https://onco.cc/cancers/all-leukemia/), [Acute myeloid leukaemia](https://onco.cc/cancers/aml/), [Chronic myeloid leukaemia, accelerated and blast phase](https://onco.cc/cancers/cml-advanced-phase/), [Chronic myelomonocytic leukaemia and MDS/MPN overlap neoplasms](https://onco.cc/cancers/cmml/), [Myelodysplastic syndromes / neoplasms (MDS)](https://onco.cc/cancers/mds/)
- fronts: [Diagnostics & Biomarkers](https://onco.cc/fronts/diagnostics/)

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