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BRCA – the need to know about the “breast cancer gene”

Type “Angelina Jolie effect” into Google and the first two articles (at time of writing) link to a pair of scientific papers describing a phenomenon that couldn’t be more enticing for the media. Click-bait headlines aside, this effect is real and refers to the impact that Angelina Jolie had on boosting the number of people accessing genetic testing to see if they were at greater risk of breast and ovarian cancer. Jolie’s high-profile public announcement that she had had a preventive double mastectomy after finding out she was a carrier of a mutation to a gene called BRCA1 ultimately led to a greater awareness of BRCA genes and their link to cancer. But what’s the real story behind the BRCA genes?

What are the BRCA genes?

The genetic code contained within the DNA of each and every cell of your body is like one giant recipe book. Within the book are chapters called genes, which are the instructions a cell uses to build biological molecules called proteins. There are two chapters on BRCA in the human genetic recipe book, one called BRCA1 and one called BRCA2, both of which are the instructions a cell needs to make proteins of the same name.

Both of these proteins play a pretty important role in cells as their function is to help repair damage to DNA, and importantly kick-start a self-destruct process in a cell if the damage is beyond repair. This is crucial because damaged DNA that goes unchecked can lead to genetic mutations that cause cancer.

What’s the problem with having a faulty BRCA gene?

Mutations to genes can end up “re-writing” the instructions contained within the genetic code. Sometimes when this happens the cell can no longer “read” the instructions properly and crucial proteins are left unmade or built incorrectly so they don’t work. A bit like trying to bake a cake without a working oven.

Cells that don’t have working BRCA proteins due to a fault in the gene are missing a vital piece of the cellular machinery used to repair DNA, and so there is an increased risk that harmful damage accumulates in cells, which could ultimately lead to cancer.

Epidemiological studies that look at the effects of something on a large population have shown that carrying a faulty BRCA gene can increase your risk of breast, ovarian and prostate cancer. For example, it’s estimated that between 55 and 65 percent of women who carry a harmful fault in the BRCA1 gene will develop breast cancer by age 70.

Can a faulty BRCA gene be passed on to your children?

It’s been scientifically documented since the 1940s that breast cancer appears to run in families hinting that there is a heritable genetic component to the disease. It wasn’t until much later, once the BRCA genes had been identified, that it was clear that faulty version of the genes can be passed through generations. These genes are not the entire story though as they only account for 20 to 25 percent of all cases of hereditary breast cancer, and only 5 to 10 percent of all cases of breast cancer. Risk of cancer is complex and comes from a combination of genes, environmental and lifestyle factors. A better understanding of how all three of these interact is the key to developing a more accurate picture of an individual’s cancer risk.

How can doctors and patients make use of faulty BRCA genes?

Thanks to the discovery of the BRCA genes and advances in technology that allow us to accurately analyse a person’s DNA, it is now possible to be screened for genetic faults such as those found in the BRCA genes. This is useful because it means individuals can find out if they are at an increased risk of certain cancers, and if so, allows them to make decisions about how they might be able to manage their risk. Angelina Jolie, for example, decided to have preventive surgery in order to drastically reduce her chance of breast and ovarian cancer.

Faulty BRCA genes have also emerged as a way to kill cancer cells. What seems to be a cause of cancer, can also be used to treat it. Cancer cells also need to repair their DNA as too much damage can also cause them die, just as it does to normal cells. However, if they don’t have BRCA proteins to repair DNA they rely more heavily on other ways to do so. Drugs that block these alternative ways have turned out to be a pretty effective way to target cancer cells that have a faulty BRCA gene. PARP inhibitors are a type of drug that do just this (you can read more about them here), and one PARP inhibitor, called olaparib, is approved for use in the treatment of some types of ovarian and breast cancer.

Image credit: Gage Skidmore/Flickr

Science Communications Manager

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