Different types of lab tests are used to diagnose cancer and help plan treatments.
Doctors use imaging tests, lab tests, and other procedures to help diagnose cancer. The tests they use depend on the type of cancer doctors suspect and where it may be located in the body. Laboratory tests help the care team learn more about your child’s cancer and plan treatment.
How samples are collected
Small amounts of fluid and tissue are often used for testing. These are called samples or specimens.
Blood tests and bone marrow tests help diagnose many blood cancers. A biopsy helps diagnose many solid tumors and other cancers.
Blood cancers (leukemia and lymphoma)
For a blood sample, a health care provider takes a small amount of your child’s blood from a vein. Bone marrow samples are collected through a bone marrow aspiration or bone marrow biopsy.
Solid tumors
When doctors think a patient may have a mass or abnormal growth, they often start with imaging tests, such as:
If tissue needs to be examined more closely, the care team may do a:
Needle biopsy: A needle is used to remove a small tissue sample.
Surgical biopsy: Part of the tissue is removed during surgery.
Resection: As much of the tissue as possible is removed during surgery.
What happens to the sample in the lab
The pathology lab prepares the tissue sample and examines it in different ways. A pathologist is a doctor who looks at cells, tissues, and body fluids to help diagnose disease. The pathologist uses what they learn to create a report for your child’s care team.
Gross examination
First, the pathologist examines the sample without a microscope. They look at things such as its color, size, and shape.
Preparing the tissue
Next, the tissue sample is prepared so it can be examined under a microscope. There are 2 main ways to prepare the tissue.
Frozen section: Sometimes a tissue sample is quickly frozen, cut into thin sections, and examined right away. This helps surgeons make decisions during surgery.
Permanent section: Most tissue samples are prepared as permanent sections. The tissue is processed and placed in a special wax called paraffin. This allows the samples to be cut into very thin sections.
To prepare the samples for study under a microscope, the samples are:
Cut into very thin sections
Placed on slides
Stained with dyes to help highlight different parts of the cells
Looking at cells under a microscope
The pathologist then examines the slides under a microscope. They look at:
The types of cells
How the cells are arranged
Whether cancer or signs of cancer are present
Features of the cells that help predict how fast they may grow or spread
The edges of the removed tissue (margins) to see if they are free of cancer cells
Other lab tests may be used to look for proteins, cell features, gene changes, and other signs of cancer. These results will also be included in the pathology report.
Types of laboratory tests
Pathologists may use special lab tests to learn more about a cancer. These tests can help make the diagnosis and inform treatment.
Cell-based tests
Immunophenotyping looks for specific proteins or markers on the surface of cells or inside the cells. These proteins help identify different types of cells, including cancer cells.
Immunophenotyping may include:
Immunohistochemistry (IHC): Tests tissue samples to see if certain proteins are present. It helps pathologists recognize abnormal cells. It can help confirm a diagnosis or detect relapse.
Flow cytometry: Measures large numbers of cells in a sample, shows how many cells are present, and what markers they carry
Flow cytometry is very sensitive. It can detect very small numbers of cancer cells that may remain after treatment. This is known as minimal residual disease (MRD), which can help doctors know if some cancers are likely to come back.
Genetic and molecular tests
Mutation testing looks for changes in chromosomes, genes, DNA, RNA, and proteins. These changes may cause cancer or affect how cancer responds to treatment.
DNA sequencing helps identify gene changes (mutations) that may cause cancer.
PCR (polymerase chain reaction) makes many copies of small amounts of DNA so they can be studied more easily. DNA contains the genetic information cells need to grow and function. PCR can help detect:
Cancer-related genetic changes
Infections caused by bacteria or viruses
Chromosome tests look for missing, extra, or rearranged chromosomes or genes. Chromosomes are structures inside cells that contain DNA. Chromosome testing includes:
Cytogenetics: Looks at chromosomes to find changes such as broken, missing, rearranged, or extra pieces
FISH (fluorescence in situ hybridization): Uses special fluorescent probes to look for changes in specific parts of DNA
Understanding the pathology report
The pathology report includes information about the tissue sample and test results. This report helps the care team diagnose cancer and plan treatment. It may include:
The type of cells found
Whether cancer is present
The tumor grade
Information that helps determine cancer stage
Whether the edges of the sample (margins) are free of cancer if surgery was done
Some tests are available quickly. Others take longer because the sample must be sent to another lab. Some tests require a series of steps and procedures. It may take several days or even weeks to get results.
Pathology reports are written in medical language. You may not know how to read your child’s pathology report. Your care team will explain the results and answer your questions.
How test results help guide treatment
The more doctors learn about the cancer, the better they can choose the most effective treatment for your child. Test results help the care team:
Confirm the diagnosis
Understand how the cancer may behave
Choose treatments that are most likely to work
Monitor how well the treatment is working
Sometimes, test results can also help doctors identify treatments that may not work well for a certain type of cancer.
Questions to ask your care team
What tests does my child need, and why?
What are these tests looking for?
If my child needs a biopsy, how will the sample be collected?
Will my child need imaging tests, such as an MRI or CT scan?
How long will the tests take?
When and how will we get the results?
What will the pathology report include? Can you explain it to us?
What can these results tell us about my child’s cancer?
How will these results affect my child's treatment plan?
Will my child need any additional tests?
Key points about laboratory tests in childhood cancer
Doctors use different tests to diagnose cancer, depending on the type of cancer they suspect.
Blood cancers are often diagnosed with blood and bone marrow tests. Many solid tumors are diagnosed with a biopsy.
Pathologists examine blood, bone marrow, and tissue samples to identify and learn more about a patient’s cancer.
A pathology report includes information that helps the care team diagnose cancer and plan treatment.
Laboratory test results help doctors choose the best treatment and monitor how well it is working.
Your child’s treatment for cancer depends on their diagnosis. Learn more about chemotherapy, radiation, surgery, immunotherapy, and stem cell transplant.
Some people have gene changes or genetic predisposition that increases the risk of cancer. Learn about inherited risk and genetic testing in pediatric cancer.
