Today, genomic tests are the most advanced type of research for the diagnosis of cancerous tumors. How to choose the most suitable test, and what information can you get from it? Professor Friedman, director of the oncology department at Sheba Medical Center, explains:
What we call «cancer» is more than 200 various diseases that differ in the genetic characteristics of cancer cells. In fact, every cell in the body stores genetic information that gives it instructions: how to function, develop, and reproduce. This information is stored in DNA, that is, in genetic material that is inherited. All cancers are caused by the accumulation of acquired mutations (somatic mutations) in certain genes. Only a small proportion of cancer patients (up to 10 percent) have a mutation in a single gene associated with tumor risk, leading to high cancer risk. Mutations in the BRCA1/2 genes associated with breast and/or ovarian cancer are classic examples of such genes. It should be noted that damage to genetic material occurs during life, including as part of the aging process, as a result of smoking, exposure to ionizing radiation or carcinogenic substances, etc.
The different genetic characteristics of tumor tissue in different types of cancer affect how it is diagnosed and treated. While genetic testing in a blood test (which checks for mutations that are inherited) can reveal congenital genetic mutations in certain genes, genomic tests on tumor tissue check for multiple mutations and significant genetic changes in tens or hundreds of genes simultaneously to identify unique genetic characteristics of cancer cells. It is a kind of «genetic imprint» of a cancerous tumor. In such a way, the information they provide can influence treatments, and sometimes also predict how likely a tumor is to respond to a particular treatment.
HOW ARE GENOMIC TESTS CONDUCTED?
There are two ways to perform a genomic study of a tumor: using a tissue sample, i.e. when taking a biopsy of cancer or its metastases, or using a blood sample, also called a «liquid biopsy.»
«Genomic tumor test is a test designed to diagnose the genetic tissue of aggressive tumors and tumors that do not respond to certain treatments and continue to develop despite chemotherapy or other treatments,» says Professor Eitan Friedman, founder and head of the Oncology Department of Sheba Medical Center. «Another recommendation for genomic testing is in a situation where a mutation is known in a gene or several genes that are in a tumor, to make therapeutic decisions with other drugs, such as biological ones, that can slow down or suppress the development and spread of cancer.»
HOW DO YOU KNOW WHICH TEST TO CHOOSE?
«The test is conducted according to the clinical needs and the availability of biological material,» explains Professor Friedman. «The decision to perform a test is clinical and is made by the treating oncologist and the patient together. There is a certain probability that the test results will affect the type of treatment given to the patient. For research, it is not necessary to use «fresh» tissue. It is possible to conduct tests on the material preserved in the paraffin block. Naturally, the most accurate option is to examine the tumor tissue itself, but if a biopsy is technically difficult or impossible, for example, in the case of a patient with lung cancer, a biopsy of which could damage the lung or even endanger the patient’s life, then a liquid biopsy can be performed.»
WHAT INFORMATION WILL BE OBTAINED IN THE REPORT AFTER THE CHECK-UP?
«The information obtained provides a complete genomic picture of the main genes involved in the formation and proliferation of tumors. The genomic test scans for genomic changes and mutations of various types of hundreds of genes», explains Professor Friedman. «Besides, the genomic test gives an overall picture of the mutational load in the tumor and a condition called microcrystalline instability. These are the two indicators of high practical importance in terms of determining the continuation of the patient’s treatment.»
It is important to consider that while performing a liquid biopsy, a situation may arise when a malignant tumor does not release enough tumor DNA into the bloodstream. Then the test will have to be repeated on a tissue sample.
WHERE ARE SAMPLES SENT, AND HOW LONG WILL IT TAKE TO GET RESULTS?
«The tests can be performed in any certified laboratory, both in Israel and elsewhere in the world,» says Professor Friedman. “Tests are sent to laboratories according to the type of tumor, the size of the available tissue, the qualifications of the laboratory, and other factors that influence the decision. The results will be received within a few weeks.»
IS THE TEST APPROVED BY THE HEALTH AUTHORITIES?
“The test can be approved in various situations. For example, for patients with non-small cell lung cancer, a broad genomic test is included in the Israeli health basket. Ovarian cancer patients undergo a targeted test with appropriate markers for ovarian cancer and are included in the basket. In some cases, the test is not included in the health basket and can only be conducted for a certain fee,» says Professor Friedman.