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Diagnosis and tests

Where molecular tests matter most

The related article (“Molecular tests: PCR and NGS”) explains genetic tests in general. This topic shows which molecular tests matter most in each main type of leukaemia, and why.

Last updated: ~1 min read
Four panels — Where molecular tests matter most
Figure 1.Four types, four genes.

01Short answer

Molecular tests find small changes in DNA or RNA: mutations and fusion genes. In AML, genes such as FLT3, NPM1, IDH1/2, CEBPA and TP53 define risk, and there are targeted medicines for some mutations, so results are needed quickly. In APL, confirming PML::RARA changes treatment. In CML, BCR::ABL1 shows both the diagnosis and, through quantitative PCR, the response to treatment; if the response is lacking, ABL1 kinase mutations are checked. In CLL, IGHV mutation status and TP53 changes are considered when choosing treatment. In ALL, BCR::ABL1 and “Ph-like” changes matter, as does measuring MRD. In children, some inherited predispositions may also be checked.

02Simple explanation

AML: FLT3, NPM1, IDH, TP53.

CML: tracking BCR::ABL1.

CLL: IGHV, TP53.

03Scientific explanation

Speed: in AML, some molecular results (FLT3, for example) can affect whether a targeted medicine is added in the first week of treatment.

Quantitative PCR: the BCR::ABL1 level is expressed on an international scale and shows the depth of response in CML.

04What happens in the body?

Each type has its gene

Each leukaemia has gene regions that matter most.

PCR

A tiny piece of DNA is copied millions of times.

DNA multiplying — Where molecular tests matter most
Figure 2.PCR copying — Where molecular tests matter most

The treatment path

A gene result can steer the direction of treatment.

A fork and a DNA sign.
Figure 3.A treatment path by gene.

05A molecular test

Four steps.

DNA — Extracted from the sample.1DNAExtracted from the sample.
Reading — Genes are read.2ReadingGenes are read.
Change — A mutation is found.3ChangeA mutation is found.
Choice — The doctor decides.4ChoiceThe doctor decides.

06Type and key molecular tests

TypeKey tests
AMLFLT3, NPM1, IDH1/2, CEBPA, TP53
APLPML::RARA
CMLBCR::ABL1 (quantitative), ABL1 kinase mutations
CLLIGHV status, TP53
ALLBCR::ABL1, Ph-like changes, MRD

07Key terms

Mutation
A change in a gene.
Fusion gene
Two genes joined together.
PCR
A method of copying DNA.
IGHV
An antibody gene; its status matters in CLL.
Targeted medicine
A medicine aimed at a specific change.

08Key points

  • Molecular tests find small changes.
  • In AML they define risk and targets.
  • In CML they track response.
  • In CLL they affect treatment choice.
  • In ALL, MRD matters.
  • Your doctor interprets the result.

09Frequently asked questions

Why are AML results urgent?

Some targeted medicines are added at the start of treatment.

How often is PCR done in CML?

Your doctor sets the monitoring schedule.

Do these tests mean an inherited disease?

Most changes are only in the leukaemia cells (“Molecular tests: PCR and NGS”).

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. Why are AML results urgent?

  2. How often is PCR done in CML?

  3. Do these tests mean an inherited disease?

My questions

12Sources

  1. MedlinePlus Genetics. What is a gene variant and how do variants occur?
  2. National Cancer Institute (NCI). Definition: polymerase chain reaction
  3. National Cancer Institute (NCI). Adult AML treatment (PDQ), patient version
  4. National Cancer Institute (NCI). CML treatment (PDQ), patient version
  5. National Cancer Institute (NCI). CLL treatment (PDQ), patient version
  6. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: minimal residual disease
  7. MedlinePlus (U.S. National Library of Medicine). Leukemia
  8. MedlinePlus. Complete Blood Count (CBC)
  9. NHS. Sepsis
  10. MedlinePlus (U.S. National Library of Medicine). Bone marrow aspiration
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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