Using genetic testing to identify and lower cancer riskMay 06, 2019
By Sun Hui Wen, Lianhe Zaobao
Genetic testing can be divided into hereditary cancer genetic testing and tumour genomic profiling. The former can determine whether an individual carries a genetic mutation in hereditary cancer, providing a prediction of the risk of hereditary cancer; the latter helps identify specific genetic mutations that promote cancer growth and assists doctors in selecting drugs specifically for this mutant gene.
Medical knowledge is growing every day and with its advancement, drug treatment is constantly improving. Genetic testing is the latest development for cancer-related tests. Hereditary cancer genetic testing and tumour genomic profiling are two of the most common genetic testing methods.
Two common genetic testing methods for cancer
Shao-Tzu Li, a genetic counsellor at Cancer Genetics Service of National Cancer Centre Singapore, pointed out: "Hereditary cancer genetic testing is a genetic test to determine whether an individual carries a genetic mutation for a hereditary cancer, thereby providing a prediction of the risk of getting hereditary cancer. There are many types of genetic tests on the market, and their applications and limitations are different. Many people have the misconception that hereditary cancer genetic testing is used to test whether there is cancer. However, that is not true. Hereditary cancer genetic testing is used to confirm an individual’s or family’s history of cancer, whether it is caused by a potential single genetic mutation, and to understand its associated cancer risk, hereditary pattern, and advise on how to screen, prevent or reduce the risk of associated cancer. ”
As for tumor genomic profiling, Dr Donald Poon, a medical oncologist practising at the Mount Elizabeth Novena Hospital, pointed out that the test identifies specific genetic mutations that promote cancer growth. The test results will thus assist doctors in selecting drugs that target the identified mutant gene. Genetic mutations that will develop resistance to certain cancer drugs can also be identified during genetic testing. As such, patients do not need to spend time trying out these cancer drugs that might cause drug resistance.
Genetic mutations vs tumor or cancer cell mutations
To differentiate between the two genetic tests, Shao-Tzu Li emphasized that that hereditary cancer genetic testing is the detection of germline mutations, while tumor genomic profiling is the detection of somatic mutations.
She explained: "Germ cell mutation refers to hereditary genetic mutations. As most of which are inherited from parents, all cells in the body, including eggs and sperm, carry the same genetic mutations, and thus this mutation is also passed on to future generations. Using cancer as an example, a doctor or genetic counselor will recommend hereditary cancer genetic testing to a patient who is very young but has a family history of rare cancer or many incidences of cancer diagnosed. The results help the doctor to understand the patient's hereditary cancer risk, and thus personalize the recommendation for screening and prevention, increasing treatment options, and contributing to family genetic testing and cancer risk analysis. The direct opposite of germ cell gene mutations is somatic gene mutations. Somatic gene mutations only occur in tumors or cancer cells. It does not occur in other normal cells and they will not be passed on to future generations."
Dr Donald Poon added that tumor genomic profiling does not distinguish the hereditary characteristics of cancer. This test is mainly to determine which DNA mutation causes cancer, so that oncologists can plan appropriate treatment plans for patients. On the other hand, hereditary cancer genetic testing is used to detect hereditary germ cell mutations. These two are not the same.
Individual testing process
Shao-Tzu Li pointed out that before and after genetic testing of genetic cancer, genetic counselors will examine the patient's medical history and map the history and distribution of cancer history in family members, provide genetic cancer risk assessment, genetic testing instructions, interpretation of genetic testing results, and follow-up medical examination recommendations, psychosocial support, follow-up examinations and referrals, treatment advice and so on.
For most cancer patients or their families, hereditary cancer genes are tested via blood tests, and in some cases saliva, oral cells, or skin biopsy. For example, patients with blood cancer or bone marrow hematopoietic dysfunction will be recommended to use skin sections for lab testing. As for the test procedure of tumor genome profiling, tumor tissue sections are mostly used as samples. The purpose of the test is to identify tumor gene mutations specific to the cancer itself. This will be helpful to choose the treatment of targeted drugs for specific cancers.
Dr. Poon also said that the tumor genome profiling is mainly based on biopsy specimens taken from cancer patients or cancerous tissue sections obtained during tumor resection. In addition, it can also be tested through blood test. DNA of cancer cells will be extracted and tested. Cancer patients can benefit from tumor genomic profiling. For example, patients diagnosed with early stage breast cancer will know whether they can do without chemotherapy and whether the treatment will be beneficial for recovery. This test can also help guide advanced cancer patients to choose appropriate targeted therapies and avoid those that may not work.
Cancer patients can also receive hereditary cancer genetic testing
Hereditary cancers only account for 5 to 10% of all cancers. Shao-Tzu Li revealed that carriers of genetic mutation of the hereditary cancer may not necessarily be diagnosed with cancer, but he/she has a higher risk of cancer than the average person. Therefore, it is necessary to receive personalized cancer screening or preventive measures as soon as possible. This will help with early detection and treatment and can even reduce the risk of cancer.
The proportion of hereditary cancers varies from cancer to cancer. When an individual or family has the following symptoms, they should discuss with a doctor or genetic counselor as to whether they are eligible for the test.
- History of family cancer: Three or more relatives in the same family are diagnosed with the same or related cancers;
- Early onset cancer: A family member or relative is diagnosed with cancer when he/she is very young;
- Multiple cancer: The same family member or relative is diagnosed with more than two types of cancer.
Shao-Tzu Li also reminded: "If you are not sure whether the patient or yourself is suitable for genetic testing of hereditary cancer, you can ask the relevant medical institutions, such as the Cancer Genetics Service of National Cancer Centre Singapore. Those who are already diagnosed with cancer can better understand if your cancer is a hereditary or not, to help with choice of treatment and the risk of having a hereditary cancer in the family."