Hereditary breast-ovarian cancer (HBOC) refers to cancer running in families with breast cancer and or ovarian cancer. In such families we suspect a hereditary factor (gene mutation) to cause breast and ovarian cancer occurrences in that family.
The two most common genes that are known to cause HBOC are BRCA1 and BRCA2.
- BRCA1 is a tumour suppressor gene that was first described in 1990. BRCA 1 mutation carriers have up to 40% lifetime risk of ovarian cancer and 60% lifetime risk of breast cancer.
- BRCA2 mutation carriers carry a 15% lifetime risk of ovarian cancer and a 45% chance of breast cancer.
Risk assessment includes a family tree (pedigree) but family history has a false negative in half of the cases. It is especially misleading in small families, in families with a low number of females, in families with adoption or if non-paternity could be an issue.
Genetic testing is recommended if the woman carries a higher than 10% risk of carrying BRCA1 or BRCA2. Genetic testing involves a consultation with a clinical geneticist and a simple blood /saliva test. It is available through GHNZ (publicly at no cost; however strict eligibility criteria apply) or privately (cost ~ $1500).
The advantages of genetic testing include:
- BRCA carriers may not only be at risk of ovarian or breast cancer but for both. Hence, a patient who was diagnosed with BRCA-related ovarian cancer previously is at very high risk of developing breast cancer subsequently and will benefit from enhanced breast screening or prophylactic surgery.
- BRCA carriers may pass the gene on to their sons and daughters who can be pro-actively manage their risks if tested positive.
- BRCA carriers respond well to PARP Inhibitors, which are a new class of cancer drugs. Hence, the outcomes of genetic testing may influence the selection of cancer medication.
15% of ovarian cancers are BRCA-related (inherited), which is larger than originally estimated (Australian Ovarian Cancer Research). All patients with high-grade, serous ovarian cancer should be tested for BRCA1 and BRCA2. The implications for the patient and her family are outlined above. Women with a strong family history of ovarian cancer or a personal history of breast cancer, in the absence of a known mutation, may also be at increased risk and may benefit from risk reducing surgery after appropriate review. Age of onset: The risk of developing ovarian cancer in BRCA1/2 carriers is dramatically higher than in the general population. The ovarian cancer risk associated with BRCA1 or BRCA2 increases with age. BRCA1 typically becomes aggressive from age 40 years of age onwards. Women diagnosed with BRCA2 need to take action from age 45 years. For young women should consider risk-reducing surgery 5 years younger than the youngest relative diagnosed with BRCA-related cancer. What clinical management options are available to BRCA carriers? Breast
- Breast cancer screening (ultrasound, MRI), prophylactic surgery (mastectomy). I would always refer to a breast surgeon that has an interest in high risk patients
- Screening (ovarian surveillance) does not improve pick up or survival. Ultrasound and tumour markers frequently are unreliable. Blood tests can be falsely elevated and alarming in benign conditions.
- The Oral Contraceptive Pill (OCP) reduces ovarian cancer risk by 50%.
Risk-reducing prophylactic surgery is >90% reliable and definitely recommended for postmenopausal women and those who have completed their family. Prophylactic surgery also reduces the risk of breast cancer. The earlier the ovaries are removed the higher is the protection against breast cancer (before or at 40 years old).