Everything you need to know about hereditary breast and ovarian cancer

We all have thousands of genes that provide the instructions for our bodies to function optimally.

All cancers begin when changes occur in our genes. A change in a gene that disrupts its function is called a ‘mutation’, a “gene fault” or a ‘pathogenic variant’. Cancer usually results from an accumulation of many mutations. Most of the time, those mutations are confined (at least initially) to genes in the cells of the organ or tissue where they started. We call these type of genetic mutations ‘somatic’. Somatic mutations are not inherited from our parents, and they are not passed down to our children. This is why the majority of cancers do not ‘run in families’.

A small number of people are born with a gene fault or mutation that increases their chance of developing certain types of cancer.

In these people, cancer can get a ‘head start’ because when the first mutation is inherited from a parent it is present in every cell of a person’s body. This does not mean that a person will develop cancer in every cell of their body. In fact, we know that even when people are born with these gene faults or mutations, it is not guaranteed that they will develop cancer, but they are at a higher chance of developing certain types of cancer, depending on which specific gene is involved.

• Individuals who have been diagnosed with breast cancer at a young age (under 50-years-old)
• More than two relatives on the same side of the family who have also been diagnosed with breast cancer
• Relatives who have had ovarian cancer, prostate cancer or pancreatic cancer, especially if they were young at the time of diagnosis
• Males relatives who have had breast cancer
• Ashkenazi Jewish ancestry (Jewish ancestors who came from central or Eastern Europe)

Sometimes, even in the absence of any of these features, a woman whose breast cancer has specific features (such as ‘grade 3 triple negative’ breast cancer, which has no receptors for oestrogen, progesterone and does not over-express the HER2 protein) may be at increased risk of having a hereditary predisposition to breast cancer.

Sometimes, even in the absence of any of these features, a woman whose cancer has specific features (a high grade serous ovarian cancer, or a cancer arising in the fallopian tube or the peritoneum) may be at increased risk of having a hereditary predisposition to ovarian cancer. Sometimes genetic testing is performed on the DNA from ovarian tumours by oncologists, to help determine which drugs would work best to treat the tumour. If this genetic testing finds a mutation in an ovarian cancer predisposing gene, such as BRCA1 or BRCA2, follow up genetic testing on DNA from a blood sample is recommended to find out if the mutation that was found in the tumour is somatic (i.e. has arisen in and is confined to the tumour) or if it is inherited.

Sometimes a special protein-staining test is performed on ovarian tumours. If this special test reveals that certain proteins are missing in the tumour, follow up genetic testing on DNA from a blood sample is recommended to find out if the person might have Lynch syndrome (an inherited predisposition to bowel, uterine and ovarian cancer). If you have been diagnosed with ovarian cancer, ask your doctor whether they feel that genetic testing would be indicated for you. It will be helpful if you can collect information about your family history of cancer prior to having this discussion. Your doctor may organise genetic testing for you directly, or they may refer you to a genetic counsellor/genetics clinic or familial cancer service to have this done.