(SciShow theme)

What would you do if you found out that cancer could be lurking in your genes?

More people are getting news like that these days as more kinds of cancer are being linked to specific genes and genetic tests let doctors screen your individual genomes for signs of susceptibility to the disease. But what if one of those tests comes back positive? Does that mean you're going to get cancer? Is there anything you can do? Is your DNA your destiny?

Consider the case of Angelina Jolie who just announced that she'd had a double mastectomy because genetic tests had revealed that she carried a mutation in one of her genes that predisposed her to breast cancer.

Thousands of women in the United States make the same decision every year. And that makes sense in a lot of ways. A study at the University of Texas in 2009 found that 70% of women who tested positive for genetic mutations related to breast cancer thought that preventative mastectomy was the most effective way to reduce their risk.

What's interesting is that almost all of these women said that their decision was motivated not necessarily by wanting to be healthy or to live longer, but to simply rid themselves of the fear that they'd felt since they got their test results. 65% of them said that getting mastectomies was the only way to reduce their fear of getting cancer. It's as if they were surgically having their fear removed.

Now, we're talking about cancer here, so obviously, our decisions about how to handle it and our bodies are going to be fraught with emotion, but a look at the bigger picture here shows that being genetically at risk is by no means a death sentence, and there's a whole spectrum of options for treatment.

The mutations we're talking about occur on genes that everyone has, women and men, called BRCA 1 and 2. In the 1990s a biotech company found that certain mutations on these genes predisposed their carriers to breast and ovarian cancer. The company actually patented the genes and developed tests to identify some of the dangerous mutations.

Now according to the National Cancer Institute, about 12% of all women will develop breast cancer sometime during their lives, but for women who have  inherited a harmful mutation of one of those genes, the risk is about 60%, five times higher.

Similarly, the risk for ovarian cancer among the overall population is just 1-2%, but for women with BRCA mutations it could be 20-40% depending on what kind of mutation they've inherited. However, the first thing to keep in mind is that these mutations are really rare, only 0.1-0.2% of the general population carry either the BRCA 1 or 2 mutation. And even though the odds of developing cancer are greater if you have one of them, it's an increased risk, not a diagnosis of disease. After all, 40-80% of women who are genetically at risk don't end up getting either breast or ovarian cancer.

Maybe more importantly, genetic mutations are by no means the only cause of breast cancer. In fact, BRCA mutations account for just 5-10% of breast cancer cases, and 10-15% of ovarian cancer among white women in the United States. Other causes vary widely, from behavioral factors like smoking to epigenetics, the role that your environment plays in how your genes are expressed.

And for those who do carry mutated BRCA, mastectomies aren't the only treatment. Some women opt for regular testing like frequent mammograms, breast MRIs, and clinical breast exams to look out for symptoms. And since some breast cancers are fueled by the hormone estrogen, scientists are also looking at estrogen blocking drugs as a way of preventing the disease.

As depressing and terrifying as it may be to find that you could be predisposed to an incurable disease, there are options and therefore hope. And you have options, because unlike a generation ago, today we can hear what our genes are telling us and seek out treatment before we even have a disease.

Thanks for watching this episode of SciShow! If you have any ideas or questions or comments for us, we're on Facebook and Twitter and of course down in the comments below, and if you want to keep watching, you can go to youtube.com/scishow and subscribe.