Molecular testing


Molecular testing is a type of laboratory testing that searches for specific changes in the genetic material (DNA or RNA) or proteins inside your cells. These changes can help doctors better understand the cause of a disease, how it might behave, and which treatments are most likely to be effective. Molecular testing is often performed on tissue or fluid samples collected during a biopsy or surgery, and the results are typically included in your pathology report.

Why is molecular testing performed?

Molecular testing helps reveal important details about your diagnosis that might not be visible under a microscope. It is especially useful for:

  • Identifying specific types of cancer or genetic conditions.
  • Determining how aggressive a disease might be.
  • Predicting how the disease may respond to certain treatments (such as targeted therapies or immunotherapy).
  • Detecting inherited genetic conditions that may affect you or your family.

In some cases, molecular testing can also help detect very small amounts of disease that remain after treatment.

What kinds of diseases are tested using molecular methods?

Molecular testing is most commonly used in cancer diagnosis and treatment. For example, it may be used to:

  • Look for mutations in lung cancer, colon cancer, melanoma, and other cancers that help guide treatment.
  • Identify certain subtypes of leukemia, lymphoma, or sarcoma.
  • Confirm or rule out inherited conditions (such as Lynch syndrome or BRCA mutations).

It is also used for other medical conditions, such as detecting infections caused by bacteria or viruses or diagnosing rare genetic diseases.

How is molecular testing performed?

Molecular testing is usually performed on tissue samples obtained from a biopsy or surgery, but it can also be done using blood or other body fluids. Specialized laboratory techniques are employed to analyze genes, RNA, or proteins within the cells. Common types of molecular tests include:

  • Polymerase Chain Reaction (PCR): Amplifies small amounts of genetic material to identify mutations or infections.
  • Next-generation sequencing (NGS): Analyzes many genes simultaneously to detect multiple mutations or genetic changes.
  • Fluorescence in situ hybridization (FISH): Uses fluorescent markers to detect specific genetic abnormalities.
  • Immunohistochemistry (IHC): Although it is not a molecular test on its own, IHC is commonly used alongside molecular testing to identify specific proteins.

The kind of molecular test used depends on the disease being studied and the information your medical team needs.

Is molecular testing the same as genetic testing?

Molecular testing and genetic testing are closely related, but they are not exactly the same. Molecular testing broadly refers to any test that examines DNA, RNA, or proteins, often in the context of diseases like cancer. Genetic testing typically refers to tests that look for inherited changes in your genes—changes you were born with and may pass down to family members. In some cases, molecular testing can detect both inherited (germline) and acquired (somatic) mutations, depending on the sample type and test purpose.

How does molecular testing contribute to personalized medicine?

Molecular testing plays a key role in personalized (or precision) medicine. Instead of treating all patients with a disease the same way, doctors use molecular testing to customize treatment based on each person’s specific condition. For example, if molecular testing reveals that your tumor has a mutation that responds to a certain drug, your doctor may suggest that treatment instead of standard chemotherapy. This method helps improve effectiveness and reduce side effects.

Molecular testing for biomarkers

A biomarker is a molecule or feature in your body that gives information about your health or disease. Molecular testing often searches for specific biomarkers that can help:

  • Confirm a diagnosis.
  • Predict how aggressive a disease may be.
  • Identify treatments that are more likely to work.
  • Determine if a clinical trial may be a good option.

Examples of common biomarkers in cancer include:

Your pathology report might include details about these biomarkers and their significance for your care.

What do molecular test results mean in a pathology report?

Your pathology report might include molecular testing results along with the primary diagnosis. These results might mention:

  • Specific genetic mutations or rearrangements.
  • Whether the tumor expresses specific markers.
  • Whether the results suggest a good response to certain medications or clinical trials.

Your doctor will use this information to customize your treatment plan for your specific type of disease, potentially improving outcomes and minimizing side effects.

Questions to ask your doctor

  • Was molecular testing done on my biopsy or surgical sample?
  • What did the results of the molecular test indicate?
  • Do these results impact my treatment options or prognosis?
  • Are there any targeted therapies or clinical trials based on my results?
  • Should I or my family think about genetic counseling?
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