How does genetic testing for cancer work? Understand and see benefits

You genetic testing play a fundamental role in both prevention and early detection and on deciding the best treatment for the tumor . This type of test looks for inherited changes in genes that may be related to a greater risk of developing cancer.

According to Inca (National Cancer Institute), cancers associated with genetic and hereditary factors account for around 5 to 10% of all cancer cases. The genetic mutation is transmitted from generation to generation and, when identified, indicates a greater risk of cancer in a family.

There are several types of cancer whose genes that suffer these mutations are already known, such as breast, intestine, pancreas, stomach, lung, kidney and melanoma cancer for example.

Genetic tests will be used to identify whether or not there are changes in these genes, suggesting a greater risk or not for the development of cancer, or indicating the origin of an already identified tumor. Next, understand everything about genetic tests, how they work and when they are indicated.

Types of genetic tests and their indications

There are two main types of genetic tests, as explained by Fernando Moura, oncologist at Hospital Israelita Albert Einstein: genetic prediction and that of hereditary predisposition to cancer .

The first can be performed by any healthy individual who is interested in understanding whether they have genetic changes related to cancer and serves as a form of prevention . “If I find any of these changes related to cancer, I can take actions to reduce the risk of developing the tumor”, explains the specialist to CNN .

One of the famous examples of how this test can help with prevention is the case of actress Angelina Jolie. In 2013, the artist received a positive test for mutation in the BRCA1 gene , which indicates a high risk of developing breast cancer and ovarian cancer throughout life. Based on this result, the actress opted for bilateral prophylactic mastectomy, that is, the removal of the mammary gland to reduce the risk of developing the tumor.

“This is just one example, but the test can also find mutations in genes related to other types of cancer, such as pancreatic cancer,” explains Moura. “In this case, if a test comes back positive, we can carry out further tests to analyze changes in the pancreas itself, such as MRI or ultrasound, and, if there are natural changes in the organ, surgeries are requested. If there is no change, the recommendation is to monitor the patient”, he adds.

The test of hereditary predisposition to cancer could it be recommended for people who have already been diagnosed with the disease and serves as tool for decision making focused on treatment.

“For example, in breast cancer, there are certain characteristics in which we need to do the test to understand if the cancer is sporadic, that is, it happened randomly, or if there is a possibility that the patient has some genetic family inheritance that led to the disease”, explains Moura. “In triple-negative breast cancer, which is a subtype of the disease, this genetic test is recommended”, he explains.

In this case, genetic testing will be useful to evaluate the best type of treatment to be carried out for cancer . Furthermore, it serves as an indicator for other people in the patient's family, such as parents, children or siblings, to carry out the test to identify whether they also inherited the genetic mutation.

How is genetic testing performed?

Genetic tests are generally ordered by a doctor. It is made from a small sample of body fluid, which can be blood or saliva, or tissue, such as inner cheek cells and skin.

This sample is sent to a laboratory that specializes in genetic testing and the results are returned to the doctor who ordered the test. “The ideal is to have the support of an oncogeneticist in this process. It is essential to explain how the exam is carried out before it is carried out and also afterwards, to correctly interpret the results found”, emphasizes Moura.

It is also worth mentioning that genetic tests may vary depending on the clinic or hospital in which they are carried out. “These tests are very varied in terms of quality and the number of genes that can be detected, around the world”, says the oncologist. “At Einstein, for example, the test can evaluate more than 500 genes for 22 types of cancer”, he explains.

How to interpret the results of a genetic test?

The results may vary according to the type of genetic test, as explained by Moura.

In genetic prediction tests (done by healthy individuals), the results are binary:

• Positive : there is a risk of developing cancer;
• Negative : There is no risk of developing cancer.

“The result comes like this: 'we analyzed the risk of developing breast cancer due to a mutation in the ATM gene', for example”, says the oncologist. He explains that the results only indicate the prediction of cancer and not that the patient will necessarily have the disease. “The result explains the percentage chance of tumor development based on the mutated gene found,” he says.

In cases of genetic predisposition tests for cancer, carried out on people already diagnosed with the tumor, the possible results are:

• Pathogenic variants : hereditary changes in the gene that are related to tumor development;
• Likely pathogenic variants : hereditary changes in the gene that may be related to the development of the tumor;
• Variants of uncertain meaning : hereditary changes in the gene that it is not yet known whether or not they can increase the risk of developing the tumor;
• Probably benign variants : hereditary changes in the gene that may be unrelated to the tumor;
• Benign variants : hereditary changes in the gene that are unrelated to the tumor.

Benefits and limitations of genetic testing

The main benefit of carrying out genetic testing is, in Moura's view, “opening the possibility of screening for different types of cancer”. “Imagine that an individual tested positive for the BRCA gene when diagnosed with pancreatic cancer. I will recommend that his family also undergo the test, because their family members may carry the mutation and, with the test, we will have control and better monitoring by requesting regular tests”, he explains.

However, the expert states that there are still limitations, mainly regarding access to genetic tests. “We still have a lot of difficulty in supplementary health ensuring access to tests for patients. We also have difficulty guaranteeing access to oncogeneticists, as not all cancer centers have this structure and we, oncologists and hematologists, often do not have enough preparation to guide a patient about genetic tests”, he adds.

Furthermore, there is still no full access to genetic tests through the SUS (Unified Health System), which also makes it difficult to carry out tests on patients with lower income. Genetic tests can range from R$2,000 to R$4,000, on average.