Genomic testing refers to new tests that are available to obtain information about the DNA-related characteristics of a tumor. Cancer is a disease caused by certain changes in the genes that control how our cells grow and function. Genes are made up of DNA and carry instructions for making proteins that control how our cells behave. Changes, such as mutations in the genes or a change in the number of genes, can cause cells to make too many proteins or cause proteins to not function properly. These proteins can cause normal cells to grow out of control and become cancerous.
Genomic testing can identify specific genetic changes in the DNA of cells that cause cancer cells to grow. Some of these specific changes in the DNA require specific drugs that work to block further alteration. So by identifying the genetic changes in the DNA of your cancer cells, doctors can recommend new targeted therapies that attack your mutations.
For many years, cancers have been categorized by the organ in which they begin (i.e. breast, lung, colon, prostate). As we learned more about how cancers develop, grow, and spread, researchers have begun to categorize cancers in terms of their specific genetic changes. These genetic changes, as mentioned above, fuel the growth and division of cancer cells. This new way of viewing cancers has already fostered the development of groundbreaking new "targeted" treatments.
Targeted therapy is becoming more common, and HER2 and BRAF targeted therapies are just two examples. Research is ongoing to identify more genetic changes and specific treatments. However, there is no indication where the targeted therapy will work.
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Today, surgery, chemotherapy, and radiation therapy are still the standard of care for many cancer patients. These therapies have advanced greatly over the years, but still have many severe side effects and do not help everyone. Genomic testing allows physicians to find specific genetic changes in the DNA of a patient’s tumor, and identify targeted therapies that are more likely to help the patient.
A targeted therapy may be less harmful to healthy cells and more effective than traditional chemotherapy. They often have different side effects. Targeted therapies or precision medicines are designed to block a specific target, usually a protein or genetic change. Since targeted therapies directly attack the alteration in the cancer cells, they may have fewer side effects than traditional medications such as chemotherapy.
Genomic testing may be recommended to patients whose cancer does not respond to standard treatments such as chemotherapy, radiation therapy, and/or surgery. Genomic testing may also be used when the cancer diagnosis is unclear. Genomic testing can help doctors identify targeted therapies that may be beneficial to the patient. Talk to your doctor about whether genomic testing is right for you.
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DNA is the basic building block of genetic material that is present in every living organism. DNA carries instructions that tell the cells in our bodies what to do. The complete set of DNA in your cells is called your “genome”. Each DNA strand is made up of a sequence of base pairs. There are four bases: A – adenine, T – thymine, G- guanine, and C- cytosine. A always pairs with T, and G always pairs with C. The specific sequence of base pairs in a DNA strand determines the specific instructions for your cells. DNA strands are broken up into units called “genes” that contain instructions for every bodily characteristic and function.
When these genes contain mistakes, such as alterations in the number of genes (copy number variations) or mutations in the gene, the cells may not function correctly. These genetic “mistakes” can cause the cells to make too many proteins, too few proteins, or abnormal proteins, which can cause the cells to grow out of control as malignant cancer cells.
Genomic testing uses advanced techniques to “sequence” the DNA or RNA in a cancer cell, or map out all of the base pairs in the cell’s DNA. Doctors can then analyze the sequenced DNA and determine if any genetic mutations or alterations are present. Even a small change in the DNA of a cell can prevent the cell from functioning properly.
Each 'word' (codon) in your DNA encodes an amino acid and is three letters long. We can think of a gene as a sentence made up of three letter words. Assume the sentence “THE BIG DOG SAW THE CAT” represents a gene.
If one letter is changed, it could change the whole meaning of the sentence. For example,
If a letter is deleted or added, it causes the whole sentence to shift or have a mutation:
If the gene is “overexpressed” or “amplified”, there are too many copies of it:
As you can see, even a small change in the DNA of a cancer cell could cause the cell to receive bad instructions, that may tell it to survive and grow out of control, causing cancer.
Genomic testing aims to determine the specific molecular changes driving tumor growth in order to identify targeted therapies that may be beneficial. For certain tumor types, such as breast cancer and lung cancer, targeted therapies may already be recommended as a standard therapy. For other tumor types, research is ongoing and evolving to identify specific genetic abnormalities in the cancer cells, and to develop treatments to target these changes. In the future, it may be possible to identify a tumor’s genetic changes for any type of cancer, and to prescribe a precision therapy to treat the disease. It may also be possible to distinguish cancer types and subtypes based on molecular characteristics rather than on the organ or location in the body, allowing for more precise and effective treatment of the disease.
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