Understanding the Genomics and Genetics of Cancer


Genomic testing is revolutionizing cancer treatment by allowing doctors to treat some patients according to the unique characteristics of their cancer. This is known as precision medicine, and it offers a more patient-focused approach to cancer care. Not all doctors currently use genomic testing for every cancer type, but this specialized testing is expected to play a bigger role in diagnosing, treating and monitoring cancer now and in the future.

Use this information to learn about genomic testing and how it applies to your cancer care. This knowledge will empower you to engage in shared decision-making with your doctor.

Decoding Genomic Testing

The discovery that cancer begins at the cellular level has paved the way for the use and application of genomic testing. Scientists now understand that cancer is a disease of our genes, which are pieces of DNA in our cells. DNA refers to the molecules inside cells that carry genetic information that is passed from one generation to the next through offspring. Almost every cell in the body contains a complete copy of the genome, which contains all the information needed for a person to develop and grow.

Cancer forms when genes begin to change, or mutate, within the structure of normal cells. The foundation of genomic testing is built on finding those mutations. It is important to understand that just as every person has a specific mix of genes that is unique to them, cancers are driven by a mixture of specific mutations. Understanding the types of mutations your tumor has will help you make informed decisions with your doctor about your treatment options.

Genomic testing is a broad term that refers to looking at a cancer’s biomarkers from a biopsied tumor tissue or a blood sample. Also known as molecular testing or tumor profiling, it is performed in a laboratory in an attempt to detect biomarkers, which are substances such as genes or molecules that can be measured in the blood, plasma, urine, cerebrospinal fluid or other body fluids or tissues. They are produced by cancer cells or other cells of the body in response to cancer.

Biomarkers are routinely tested for in certain cancers and are increasingly being used for more cancers. This type of testing allows doctors to learn about the tumor’s genome. By unlocking the DNA code of the tumor, doctors can better understand the tumor’s unique characteristics, such as the cancer’s behavior, how aggressive it might be and whether it will metastasize (spread). It also offers the possibility of treating the cancer more effectively without damaging healthy cells, as well as sparing people with slow-growing disease the side effects from aggressive treatments. If a biomarker is detected, your doctor may evaluate potential targeted therapy and immunotherapy options.

The Timing of Biomarker Testing

Biomarker testing may be performed at diagnosis, during treatment or if the cancer returns. When a tumor returns, it may have different mutations than before, which may affect treatment options and prompt another round of biomarker testing. The test(s) your doctor chooses may depend on the type of cancer you have and the known mutations associated with it (see Table 1).

In the cases where this testing has a clinical benefit, some of the additional potential uses include the following:

  • Staging a cancer
  • Determining prognosis (outlook)
  • Evaluating whether therapies are available to treat mutations in that specific cancer
  • Monitoring treatment effectiveness
  • Watching for progression or recurrence
  • Predicting how the tumor might behave, such as how fast-growing it is and how likely it is to spread (metastasize)

See Table 2 for more information about how biomarkers are used.

Table 1 - Types of Genomic Tests

Test What the test does Sample type Purpose
Comprehensive biomarker testing Looks or known biomarkers Tissue Determine treatment
Cytogenetic tests Looks for changes in chromosomes, including broken, missing, rearranged or extra chromosomes Tissue, blood or bone marrow Diagnose, plan treatment, determine treatment effectiveness
Fluorescence in situ hybridization (FISH) Looks at genes or chromosomes in cells and tissues and identifies where a specific gene is located on a chromosome, how many copies the gene are present and any chromosome abnormalities Tissue Diagnose, prognosis and evaluation of remission
Immunohistochemistry Tests for certain antigens (markers), such as proteins like PD-L1. It may also be used to determine the difference between cancer subtypes Tissue Diagnose
Immunophenotyping Tests for and identifies markers on cells Blood or bone marrow Diagnose and classify blood cell cancers
Karyotype Looks for abnormal numbers or structures of chromosomes Blood, bone marrow or tissue Diagnose and identify the Philadelphia chromosome found in chronic myelogenous leukemia
Liquid biopsy (also called circulating tumor DNA) Looks for cancer cells or pieces of DNA from a tumor that are circulating in the blood Blood Detect cancer at an early stage, plan treatment, determine treatment effectiveness, monitor for recurrence
Microarray Generates a genetic profile fora given tissue sample that reflects the activity of thousands of genes Tissue Identify cancer subtypes
Multi-gene panel testing Studies many genes in a sample of tissue to find mutations in certain genes that may increase a person's risk of cancer Blood Find cancer, plan treatment or determine treatment effectiveness
Next-generation sequencing Tests multiple genes simultaneously Tissue Diagnose, prognosis and plan treatment
Polymerase chain reaction (PCR) Looks for certain changes in a gene or chromosome Blood, saliva, mucus or tissue Find and/or help daignose a cancer
Reverse transcription PCR (RT-PCR) Amplifies traces of DNA for accurate analysis; looks for activation of certain genes Blood, saliva, mucus or tissue Diagnose

Table 2 - How Biomarkers are Used

Purpose Description
Screening Most biomarkers are not useful for screening; only 1 biomarker (prostate-specific antigen) is used for screening
Aid diagnosis Biomarkers can help identify the type of cancer when considered along with other clinical factors, such as symptoms and findings on imaging studies
Determine prognosis Some biomarkers are factors considered when determining prognosis or predicting the outcome
Guide treatment Some biomarkers can provide information about the types of treatment that are more likely to produce a response
Monitor response to treatment Biomarkers can monitor the effectiveness of treatment, especially for advanced cancers
Detect recurrence or progression One of the primary uses of biomarkers; if the level of a tumor marker is elevated before treatment, is low after treatment and then begins to increase after treatment, it is likely that cancer is recurring or progressing

What You Need To Know

Knowing whether your cancer has any biomarkers may help you take a more active role in treatment planning. This approach to treating cancer is more personalized and precise than traditional treatment strategies. It may be challenging to process all of the new information you receive when you are diagnosed; however, this is a good time to ask about biomarker testing and whether your doctor has already had it done or plans to. Sometimes your doctor will order biomarker testing on a tissue sample collected during a biopsy without you realizing it.

Not all cancer centers offer molecular testing, so it is important to determine whether it has been performed on your blood or tissue samples (see Have the genomic conversation with your doctor). If it was, ask your doctor to explain which biomarkers were tested for and the results. If the testing has not been performed, request it to find out whether you may have access to drug therapies that target the cancer.

Testing may be used to find one or multiple types of mutation in tumor cells. With some cancer types, it is recommended you have comprehensive biomarker testing, which looks for all possible mutations in a tumor regardless of whether drugs are available to treat these mutations. Keep in mind that not every tumor has known mutations, and some are identified that do not yet have a specialized treatment.

Looking Forward

Ongoing research is expected to continue finding more biomarkers in the future. As a result, new drugs targeting specific mutations will likely be developed. As precision cancer care evolves, comprehensive biomarker testing is expected to become more widespread and included as standard of care for diagnosing and treating many types of cancer in the future.

To be fully informed about your treatment options, learn about the types of testing available and the biomarkers for your specific type of cancer.

Have the genomic conversation with your doctor

You do not need a scientific background to understand how genomic testing results could offer treatment options that you wouldn’t know about otherwise. You simply need information. If your doctor has not brought up genomic testing, set up a time to talk about it. Ask these questions, take notes and check the boxes as you go down the list to ensure you gather as much information as you can.

  • Is genomic testing available for my type of cancer?
  • What risks and benefits should I be aware of?
  • Does insurance cover genomic testing?
  • When would this testing occur? Have I already had it as part of my blood work or biopsy? If so, did I have a single test or a comprehensive test?
  • Will you use a blood or tissue biopsy to do the testing?
  • How long will it take to get the results?
  • How will those results affect my treatment options?
  • Is it safe to wait to begin treatment until I get the results?
  • Who will help me understand the results?
  • Will I need to be re-tested again at some point?