Busting Myths About Your Genes and Breast Cancer

For starters, how common is genetic breast cancer?

DNA in test tubes

“I look just like my mother and grandmother, and they both had breast cancer. So I’ll have breast cancer, too.”

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Is the statement above based on myth or fact?

Answer: Myth. The genes that affect your physical traits aren’t the same ones that affect your breast cancer risk.

But the statement does bring up important follow-up questions. Did your mother and grandmother have breast cancer at a young age? Did other family members have breast cancer, too? Was their breast cancer confirmed as being genetic? These are all important red flags, unlike physical appearance.

That statement is just one myth among many in the world of breast cancer and genetics. Below are a few more — along with the facts you should know instead.

Myth: Most breast cancer is genetic

In truth, about 10 percent of all female breast cancers are caused by “strong” inherited genetic mutations. Men get breast cancer, too, but we don’t have an accurate number for how many cases are genetic because the rate of cancer is quite a bit lower.

So, around 1 in 10 cases of female breast cancer relate to genetic mutations. That’s a high enough percentage that we encourage all people to keep a good family medical history and watch for red flags. But it also means 9 out of 10 cases aren’t related to your genes.

“It’s true that if you have a mutation, you have a higher risk of developing breast cancer during your lifetime. But a mutation does not guarantee you will develop cancer.”

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Charis Eng, MD, PhD

Founding Chairwoman of the Genomic Medicine Institute

Myth: The BRCA genes are the only genes related to risk

You’ve probably heard of BRCA1 and BRCA2 genes. They’re the most common genes involved in breast cancer, so they get the most coverage. A mutation in these genes raises your lifetime risk of developing breast cancer to as high as 85 percent.

But there are other genes with strong links to breast cancer, too. For example, P53 mutations — while less common than BRCA mutations — can lead to an even higher lifetime risk.

There are currently 10 genes in total with strong connections to breast cancer risk: the three above plus NF1, SDHB/D, KLLN, PTEN, STK11 and CDH1. Often these genes are tied to other cancers but do raise your risk of breast cancer, too. For example, PTEN is connected to Cowden syndrome, which has a high risk of breast, thyroid and other cancers. CDH1 is tied to gastric cancer but also has a high risk of lobular breast cancer.

If this seems like a confusing mess of alphabet soup, never fear: That’s what genetic counselors are for. If you have red flags for genetic cancer — such as an early age of diagnosis, two or more different cancers or multiple family members who have had cancer — ask about a referral for genetic counseling.

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A genetic counselor helps determine exactly what screenings you may need, puts test results into context and helps guide you to next steps, from treatment to high-risk monitoring.

Myth: Not everyone has these genes

Actually, everyone does have two copies of these genes (a pair of working genes). Whether you’re a man or woman, you have BRCA, P53, all of the above.

You just don’t necessarily have a mutation in these genes. It’s the mutation — not the gene itself — that leads to cancer risk.

Think of these genes as editors. They search through the massive amounts of data in your cells looking for errors. When they have a mutation, they can no longer edit properly. That’s when mistakes multiply, and cancer grows and spreads.

Myth: If you have a mutation, you will automatically get cancer

It’s true that if you have a mutation, you have a higher risk of developing breast cancer during your lifetime. But a mutation does not guarantee you will develop cancer.

For one thing, if you know you have a mutation, you can act on that information. You’ll work with your doctors on a plan for monitoring and prevention. In the highest-risk cases, that may mean discussing options such as preventive surgery, too.

But beyond that, not everyone with a genetic mutation has exactly the same lifetime risk. The next step in medical research is fine-tuning our risk assessments. For example, with a BRCA mutation, we want to know exactly who has that high 85 percent lifetime risk and whose risk may be lower, based on other factors. That’s the future, and it may be closer than you think.

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Charis Eng, MD, PhD

Charis Eng, MD, PhD is founding chairwoman of the Genomic Medicine Institute and founding director of its Center for Personalized Genetic Healthcare. Dr. Eng is a global leader in cancer genetics and cancer genomic medicine.
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