Genetic testing for cancer predisposition
Cancer is a disease that is common among humans. It usually occurs by chance. 5 – 10% of cancers that affect humans are as a result of inherited gene mutation. These mutations increase a person’s chances of developing cancer significantly. Genetic testing can help people determine their chances of having cancer by searching for particular mutations in their genes, chromosomes and proteins.
These changes can be harmful, beneficial or neutral. Harmful mutations have been known to cause about 5 – 10% of all cancers. Mutations are changes that occur in a person’s genetic composition, i.e. these changes can happen in the chromosomes, genes (DNA and RNA) and proteins. Certain types of cancer can develop in a family not as a result of mutation, but as a result of exposure to some harmful environmental factors or lifestyle such as smoking or alcohol consumption.
These can lead to the development of typical cancer cases in family members living in the same environment, or having a similar lifestyle pattern. However, carrying out genetic testing can confirm whether cancers developed in family members are as a result of mutated gene, environment or lifestyle pattern.
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Genetic testing is available for the following types of cancer:
- Breast cancer
- Prostate cancer
- Colon cancer
- Ovarian cancer
- Sarcoma: cancer that can affect fat, muscle, blood vessels, cartilage, tendons, ligaments and deep skin tissues.
- Kidney cancer
- Pancreatic cancer
- Stomach cancer
- Thyroid cancer
Benefits of genetic test
- Genetic testing helps to predict a person’s risk of developing cancer and other types of diseases
- It helps to determine if a person has genes that could increase the risk of developing cancer in such person’s offspring if such genes are passed on.
- Genetic testing provides information that guides a person’s health care.
- It also helps with the diagnosis and management of cancer conditions in patients.
Categories of people that should consider undergoing a genetic test for cancer predisposition
- People who are concerned that their family history predisposes them to cancer. People in this group should see a genetic counsellor for counselling.
- People who have been diagnosed with cancer at an early age
- People suffering from different types of cancer at the same time.
- People suffering from cancer of paired organs like kidneys or breasts.
- People with first-degree relatives having similar cancer types.
- People with rare cases of cancer, e.g. breast cancer in males.
- People with birth defects associated with hereditary cancer syndromes like benign skin growths, skeletal abnormalities, etc.
- People belonging to ethnic groups linked with increased chances of developing certain types of cancer, e.g. ovarian cancer in Jews.
- People with more than one family member having cancer.
Though genetic testing is a personal decision, it is best to make such decisions with the help of family members, health care provider and a genetic counsellor.
Role of genetic counselling in genetic testing
Genetic counselling is recommended before carrying out a genetic test for inherited cancer diseases. It is also recommended that patients should be subjected to genetic counselling after receiving the genetic test result. If the test result is positive, then the patients will have to learn about the inherited cancer diseases they have been diagnosed with. Genetic counselling should be handled by a highly trained and experienced genetic counsellor or other health caregivers who are experienced in cancer genomics. Aspects covered by genetic counselling include:
- Risk assessment based on an individual’s personal and family record of hereditary cancer syndrome.
- Concerns relating to the following:
- The appropriate genetic test to undergo
- The Benefits and dangers of genetic testing
- The Implications of the test result
- The impact of the test result on the family
- The Possibility of discovering genetic mutation with no known effect on cancer.
- The concerns of transmitting mutated gene(s) to the offspring
- Details, and accuracy of the genetic test to be done and the interpretation of the test result.
- Preventive care and genetic screening recommended for the patient
- Recommendation of support group and other sources of information and resources for the patient
- Emotional support for the patient.
Before performing a genetic test, a written consent is obtained from the person by signing a consent form which clearly confirms the following:
- That the person is well informed about the test
- That the reason for the test along with the following is well understood:
- The medical implication of the test
- The risks and benefits of the test
- Other alternatives to the test
- Privacy concerns
Genetic testing: How it is done
- The genetic counsellor or other health care providers recommend the test for a person based on the person’s family history
- A genetic test option is chosen by the geneticist
- The test is carried out on a small sample of saliva, blood, cheek cells or skin cells
- The sample is mailed to the corresponding lab address
- The result is sent to the genetic counsellor who recommended the test.
Interpretation of genetic test result
A positive result
indicates the following:
- Increased chances of developing some types of cancer later in life
- For a person suffering from cancer, a positive result indicates that the cancer was more likely caused by a hereditary genetic mutation
- The need for other members of the family to subject themselves to genetic testing
A negative result
indicates the following:
- No mutation in the genetic composition of such individuals detected. It shows that the person did not inherit a mutation in his genetic makeup that can increase the person’s risk of developing cancer. This is a true negativeThis means that the person has the same chances of developing cancer along with other members of the population.
- No detected mutation in the genetic composition of a person whose family has a strong history of cancer. Although there are no records of mutation associated with inherited cancer diseases. This type of negative result is termed ‘uninformative negative.’
Negative effects of genetic testing
- The psychological effect of the positive result of a genetic test can be overwhelming on a person
- Cost of testing and additional recommended testing can be quite huge, except if it is covered by health insurance.
- Privacy concerns
Regulation of genetic tests
Genetic test labs are regulated in the US by the Clinical Laboratory Improvement Amendments
(CLIA) program. Certified labs are expected to meet up with the high standards for accuracy, quality and reliability of tests.