It is possible to detect mutations in some cancer predisposing genes. Some mutations may not be detected using current technology.
Genetic testing involves first searching for a gene mutation. The genes most commonly tested are BRCA1 and BRCA2. After genetic counselling, a sample of blood is usually taken from a woman in the family who has developed breast cancer or ovarian cancer. The DNA is ‘searched’ for a gene fault. This testing may take some months.
If a gene fault is not detected after a ‘mutation search’, then testing for the family should be considered as inconclusive. However, if a fault is detected, then other family members (men and women) can be tested to see if they carry the same gene fault or not. The testing for other family members is known as ‘predictive genetic testing’. This is a relatively quick test since the laboratory only has to determine the presence or absence of the ‘family gene mutation’ in a predictive test.
Women who carry a fault in BRCA1 or BRCA2 have a high lifetime risk of breast cancer, estimated to be in the range of 30-60%, and a lifetime ovarian cancer risk of about 20%. They can benefit from measures for prevention and early detection of cancers. Men who carry a fault in BRCA1 or BRCA2 may be at some increased risk of prostate cancer and male breast cancer. A person with a cancer-predisposing gene fault has a 50% chance of passing on the faulty gene to any child (male or female). Importantly, individuals who are found by a predictive test not to carry the family-specific gene mutation can be considered to be at the average risk of cancer. They (and their offspring) can usually be reassured that no additional cancer screening is required.
Genetic testing is offered only through a family cancer clinic. If a woman is referred to a family cancer clinic, the availability, limitations, potential benefits, and possible consequences of genetic testing will be discussed with her.