Genetic testing is focused on two scenarios in oncology. The first is prevention: a person’s genetic study is done to find out if he or she has a predisposition or a higher probability for certain types of cancer. The second is as a tool for therapeutic decisions.
Before, cancer treatment was chosen based only on the site where it occurred (breast, intestine, prostate, for example). Now, this choice is also based on genetic alterations that the tumor or the patient presents.
Genetic tests represent an extraordinary gain in the efficiency and personalization of cancer prevention and treatment. Increasingly, each patient is treated individually and not simply the disease.
Genetic testing in oncology – who should do it?
Patients who seek this type of testing usually want to know if they are carriers of a mutation that has been passed on to them hereditarily (from parent to child).
A mutation is a defect in a gene that causes it to malfunction. When an individual is born with a genetic alteration passed down from the parent, they have a higher chance of developing cancer.
There are some genes that increase the risk for breast, ovarian and prostate cancer, such as BRCA1 and BRCA2, and others related to a higher incidence of tumors located in the intestine, uterus and thyroid, among others.
Therefore, candidates for these tests include anyone who has cancer at a much younger age than that seen in the general population. For example, the age at which breast cancer most often occurs is around 55-60. But if it occurs between the ages of 30-35, there is a clue that this woman may have been born with some kind of trigger set off too early. This trigger may be genetic.
The fact that a person has several cancers (such as two different types of breast cancer, or initially bowel cancer and later melanoma) suggests that they have a low level of individual protection against the transformation of cells into cancerous, and this may be the result of a mutation that they have inherited.
Another situation is when the person has many relatives with cancer, especially on the same side of the family. This is even more suggestive when it is the same type of cancer – for example, three relatives with breast cancer in addition to the patient. What is more common, however, is that there is a diversity of diagnoses and that too many people with the disease on one side of the family attract attention. In these cases, the number of cancers that appear in the family is totally disproportionate to what would be found in the general population.
There are also some very rare types of cancer for which the doctor may indicate genetic testing and evaluate whether it is caused by an inherited gene mutation.
Genetic Testing and Cancer Prevention
Genetic testing is very helpful in cancer prevention. A person whose parent had cancer when young can be tested early and periodically to identify whether they have mutations – and, if so, take steps to reduce the risk of cancer developing. One example is breast and/or ovarian removal surgery, which occurs in very specific cases and when well indicated.
Germ tests in oncology
The genetic tests that aim at prevention are called germinative. They identify if the family has heredity for cancer.
They are preferably done before the patient develops cancer or as soon as the patient is diagnosed. In this way the patient’s family is protected, because they will know about the presence of that gene, and it is also possible to prevent recurrence (the return of the cancer in the same individual).
When a hereditary mutation is identified, it is possible to define the types of treatment that will achieve the best success rates.
Somatic tests in oncology
There are also somatic tests, in which examination is done directly on the tumor, by means of a biopsy. In this case, a study of the tumor’s DNA is performed to identify genetic defects that are not hereditary and that may offer clues as to which treatments may be more effective. Also, when the patient is not responding to treatment, this type of test can be hopeful by pointing to other avenues, such as a drug that had not been considered before.
Somatic tests tend to become more common and accessible as time goes on. Their role as tests that will be part of the initial investigation process for each cancer is unquestionable. Because their cost is still high and there are technical difficulties inherent to the reading platforms and the quality of the material that the laboratory receives, few laboratories today have the appropriate staff and equipment to do somatic panel readings. In the very near future, the improvement in the quality of specimens sent to laboratories and advances in computer technology and artificial intelligence will make this service a low-cost and indispensable test for the diagnosis and therapeutic decision of cancer.
A variant of the current somatic tests that should become popular in the future is liquid biopsy. Here, the genes of interest for evaluating the success of a treatment or for choosing a medication are evaluated directly from minute quantities of tumor DNA. This model of somatic testing allows for frequent and regular evaluation without the need for biopsies to obtain tumor material.
Availability of somatic and germline tests
Although they are expensive, genetic tests are already performed in a reasonable quantity in Brazil. But there is still a lot of room for this niche to grow, especially with the arrival of new drugs that depend on genetic alterations to be more effective and whose choice is based on the results of these tests. This is the case of target therapies and immunotherapy.
Currently, more germline tests are performed than somatic tests, because the former are included in the list of procedures covered by health insurance plans.
Laboratories which perform genetic tests
In the past, genetic tests had to be sent to other countries, since there was no infrastructure in Brazil. Nowadays, there are at least five laboratories in the country that perform the genetic tests following all the criteria and quality rigors required by international standards.
Oncoclínicas Group is one of them, because it has its own laboratory: OC Precision Medicine, which has all the monitoring and assistance from the genetics team, with physicians, pharmacists, biologists, biochemists and statisticians specialized in these types of exams. It is one of the most advanced laboratories in the country.
Genetic testing: to do or not to do, that is the question
Patients with an adequate level of information about the possibility of having a genetic cancer are usually more likely to undergo the test.
However, this is a very difficult decision for the patient. Some people want to be in control of their own health and have no doubts about agreeing to undergo the test. Others fantasize about the result and cannot tolerate the mere idea of talking about it.
In countries that practice socialized medicine, genetic testing is practically a medical decision, since it acts as prevention and reduces costs. Instead of treating a patient who already has cancer, the likelihood of cancer is identified and early preventive action is taken. This saves money on the surgery and chemotherapy that will not be needed, as well as keeping the individual economically and socially active.
People cannot forget that they are responsible for the next generations. An individual may not want to know if he or she carries a gene for cancer, but if he or she has children, he or she may pass this mutation on to them. It becomes a shared responsibility, because it becomes possible to take preventive action for oneself and one’s children.