Hereditary ovarian cancer is most commonly caused by a mutation in either the BRCA1 or BRCA2 gene. Some mutations in other genes such as RAD51C, RAD51D and BRIP1 are also known to be associated with an increased risk of ovarian cancer, but scientists have not yet found all of the genes associated with an increased risk.
How do mutations in genes cause cancer?
Genes are instructions made from DNA, which tell the cells in our bodies how to work. Every cell in our body contains genes that decide and control our body's functions, growth and appearance. Each person has two copies of most genes, one inherited from their mother and one from their father.
In general, our genes enable our cells (the building blocks that make up our body) to function normally. However, sometimes the genes that were inherited have small changes, known as alterations or mutations. If one of our genes is altered or mutated, this can sometimes result in an increased risk of developing different illnesses compared to people who don't have the genetic change.
A person with a gene mutation has a 50 per cent (one in two) chance of passing it on to their children.
What are the BRCA1 and BRCA2 genes?
The BRCA1 and BRCA2 genes (BReast CAncer genes) were discovered in the mid-1990s in families that had a lot of cases of breast cancer.
BRCA1 and BRCA2 genes are normally protective against cancer because they help repair breaks in DNA that can lead to cancer. But mutations can occur in these genes that increase the risk of developing breast cancer and increase the risk of developing ovarian cancer from two per cent (among women generally) to 30–50 per cent for BRCA1 and 10–25 per cent for BRCA2 gene mutations.
Mutations in the BRCA1 or BRCA2 genes account for the majority of hereditary ovarian cancers. About 15 per cent of women who develop ovarian cancer have a mutation in either their BRCA1 or BRCA2 gene.
It's important to note that not everyone who inherits a mutation in their BRCA1 or BRCA2 gene will develop cancer but it does substantially increase the risk.
Which other gene mutations put me at risk?
Mutations in the BRCA1 and BRCA2 genes account for the majority of hereditary ovarian cancer cases. However, mutations in other genes can also increase risk of ovarian cancer.
Lynch Syndrome (also known as hereditary non-polyposis colorectal cancer or HNPCC) is a type of bowel cancer predisposition that is linked to mutations in one of the genes MLH1, MSH2, MSH6 and PMS2. A woman with a mutation in the MLH1, MSH2 or MSH6 gene has an estimated 10 to 17 per cent chance of developing ovarian cancer at some point during her lifetime. There's a much lower or possibly no increased risk for PMS2. The chance of developing other cancers including endometrial, small bowel, urinary tract, stomach, gall bladder and pancreas can also be increased by a mutation in one of the Lynch Syndrome genes.
Mutations in RAD51C and RAD51D and BRIP1 genes can increase a woman's risk of ovarian cancer. However, these mutations are very rare. Women carrying mutations in these genes have about a five to 10 per cent risk of developing ovarian cancer by the time they reach the age of 80.
Mutations in the STK11 gene may also increase the risk of developing ovarian sex cord-stromal tumours – a different type of ovarian cancer. Mutations in this gene cause Peutz-Jeghers syndrome, which is an extremely rare condition estimated to affect one in 100,000 people. People with Peutz-Jeghers syndrome have an 18 per cent risk of developing gynaecological cancers by the age of 70.
Through ongoing research, newer genes such as FANCM are being identified, which may slightly increase susceptibility to high-grade serous ovarian cancer.
Mutations in different genes carry different increases in risk. A clinical geneticist (a doctor who specialises in genetics) or a genetic counsellor (a professional who is trained to talk to you about the benefits and risks of genetic testing) will be able to give you a more accurate and personalised risk assessment.
Last reviewed: February 2020
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