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Diagnosis and tests

Molecular tests

The related article (“Molecular tests: PCR and NGS”) explains part of the blood count. This topic looks closely at the types and purposes of molecular tests, which search for changes at the level of genes in leukaemia.

Last updated: ~1 min read
A zoom from a chromosome to DNA.
Figure 1.Zooming from chromosome to gene.

01Short answer

Molecular tests find changes at a level smaller than chromosomes: in the genes themselves. They work with DNA or RNA. The main types are PCR (“PCR”), which finds a specific gene change or fusion gene and measures how much there is; sequencing, which reads the “letters” of a gene; and next-generation sequencing (NGS) panels, which check dozens of genes at once. Molecular tests serve three purposes: to refine the diagnosis (for example the genetic subtype of AML), to assess the outlook (for example FLT3, NPM1, TP53), and to choose targeted treatment. They also measure remaining disease (MRD) after treatment very sensitively.

02Simple explanation

Gene level: smaller than chromosomes.

PCR, sequencing, NGS.

For diagnosis, outlook and treatment.

03Scientific explanation

NGS panels: in AML, FLT3, NPM1, IDH1/2, TP53, CEBPA and other genes are checked at once; the result affects the risk group.

Somatic and inherited: tests usually look for changes in the leukaemia cells (somatic); sometimes a suspected inherited tendency needs a separate test.

04What happens in the body?

From chromosome to gene

Molecular tests “zoom in” to individual genes inside a chromosome.

A gene panel

Many genes are checked in one test.

A row of glowing wells.
Figure 2.A gene panel plate — Molecular tests

Reading the letters

Sequencing reads a gene’s letters one by one.

DNA passing through a reader.
Figure 3.Sequencing reads the letters.

05How a molecular test is done

Four steps.

Extraction — DNA/RNA obtained.1ExtractionDNA/RNA obtained.
Target — Genes chosen.2TargetGenes chosen.
Reading — Sequence or amount.3ReadingSequence or amount.
Report — Changes described.4ReportChanges described.

06Types of molecular test

TestWhat it finds
PCRA specific change, a fusion, an amount
Quantitative PCR (qPCR)Amount of a fusion gene (MRD)
Sanger sequencingThe sequence of one gene
NGS panelDozens of genes at once
Digital PCRVery small amounts

07Key terms

Molecular test
A test at the level of genes.
Sequencing
Reading the order of DNA.
NGS
Next-generation sequencing.
Somatic
Present only in the leukaemia cells.
Variant
A change in a gene.

08Key points

  • Molecular tests look at genes.
  • There are several types.
  • They refine the diagnosis.
  • They affect the outlook.
  • They help choose targeted treatment.
  • They measure MRD.

09Frequently asked questions

When will the result be ready?

Some tests take days; NGS can take one to three weeks.

If I have a mutation, is my family at risk?

Most leukaemia mutations are not inherited; if there is doubt, your doctor will offer a separate test.

Why is the test repeated?

To follow the response to treatment and MRD.

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. When will the result be ready?

  2. If I have a mutation, is my family at risk?

  3. Why is the test repeated?

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. American Cancer Society. Genes and Cancer
  5. MedlinePlus Genetics (U.S. National Library of Medicine). What is a chromosome?
  6. MedlinePlus Genetics (U.S. National Library of Medicine). Can changes in the number or structure of chromosomes affect health and development?
  7. National Cancer Institute (NCI). Adult Acute Myeloid Leukemia Treatment (PDQ®) — Health Professional Version
  8. National Cancer Institute (NCI). Childhood Acute Lymphoblastic Leukemia Treatment (PDQ®) — Health Professional Version
  9. National Cancer Institute (NCI). Chronic Lymphocytic Leukemia Treatment (PDQ®) — Health Professional Version
  10. National Cancer Institute (NCI). Genetic Testing for Inherited Cancer Risk
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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