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Breast cancer genes and genetic testing: What's the story?

A genetic legacy of breast cancer in families can be worrying for patients but there are increasingly more options available to prevent the disease.

Cancer genetics hit the headlines in May when US actress Angelina Jolie announced she had undergone a double mastectomy to reduce her risk of developing breast cancer. According to her article in the New York Times, genetic testing had revealed she carried a faulty version of the Breast Cancer 1 (BRCA1) gene, giving her an apparent 87% risk of developing breast cancer. She is also at an increased risk of ovarian cancer - the disease that killed her mother at just 56. Jolie recently also lost her maternal aunt to breast cancer, highlighting the tragic genetic legacy in her family.

When discussing genes and cancer, it's important to remember that most people with cancer don't have a strong family history of the disease. There's only likely to be a strong hereditary link if a number of blood relatives are affected by the same or a limited range of cancer types - for example, families with many members affected by bowel cancer at a young age, or several cases of breast and ovarian cancer. 

The BRCA1 gene was first discovered in the 1990s, and it's one of a few genes that are known to be strongly linked to breast cancer risk - others include the similarly well-known BRCA2 gene, along with less-common defects in TP53 (tumour protein 53) and PTEN (phosphatase and tensin homolog). Inheriting a damaged version of BRCA1 increases a person's chances of developing the disease, and it also boosts the risk of ovarian and prostate cancers. 

To put this in context, the average UK woman's breast cancer risk is around 12% (one in eight), meaning that for every 100 women, 12 will get breast cancer. For 100 women carrying a faulty BRCA1 gene, between 60 and 90 of them will get the disease. Although BRCA1 gene faults are relatively rare in the population, affecting around one in every thousand people and accounting for fewer than one in 20 breast cancers in the UK, this adds up to many thousands of cases. 

Under normal circumstances, the two most common breast cancer genes - BRCA1 and BRCA2 - both carry instructions that tell our cells to make proteins that help to repair damage to our DNA - the molecule that encodes our genes. This damage accumulates over a lifetime, caused by the natural chemical reactions of life within our cells, as well as external factors in our lifestyle and environment. Inheriting a faulty version of either of these genes means that a person's cells are less able to repair this damage. In turn, this makes them more likely to pick up mistakes in crucial genes that control cell growth, leading to cancer. 

In the UK, genetic testing for faults in these genes is available on the NHS. There are quite strict criteria for eligibility, although these have recently been relaxed slightly. Testing is now offered to people who are calculated to have a 10% risk or more of carrying an inherited gene fault. This is worked out by taking a number of factors into account including a person's age, whether they have had cancer themselves, and the number of relatives affected by breast or ovarian cancer and the age at which they were diagnosed. However, the eligibility criteria are slightly different for people with Ashkenazi Jewish heritage, as there's a handful of specific cancer-causing BRCA gene faults that are known to run within this lineage. 

Deciding whether to have a genetic test - and then figuring out what to do about the results - is an intensely personal decision for a woman and her family. There are many factors to consider, such as age or whether she's had or is planning to have children. Having surgery is not the only option, and women may choose to be regularly monitored through scans. These can detect cancers when they're small and easier to treat successfully. And earlier this month, the National Institute for Health and Care Excellence (NICE) announced that women at high risk could also be offered drugs like tamoxifen to help lower the chances of breast cancer, widening the number of options available.

For anyone concerned about their family history of cancer, the first place they should visit is the GP surgery. The NHS has an excellent genetics service, and clinicians can easily refer people forward for genetic counselling and testing if they're eligible. It isn't just about the people in the patient's family who have had cancer, but also those who haven't been affected, so it can help to chat through their worries and family tree with someone knowledgeable. Cancer Research UK's cancer information nurses are always happy to talk through people's concerns and family background on the phone. 

The discovery of the BRCA genes, and others like them, was only possible through years of dedicated scientific research. Thanks to this work, people who carry faults in these genes - whether they're celebrities or regular folk - can now take positive steps to help them to overcome their genetic legacy. The research going on today, here in the UK and around the world, will bring even greater progress in understanding how our genes control our cancer risk and how this knowledge can be used to save more lives in the future.  


NICE guidelines on hereditary breast cancer 

Cancer Research UK cancer information nurses

Freephone 0808 800 4040

9am-5pm Monday to Friday