Breast cancer and DNA: 7 questions that genetic counselors get asked
October is Breast Cancer Awareness Month. It’s a time to focus on the second most commonly diagnosed form of cancer affecting women in the United States, review the strategies women (and men) should use in order to get an early diagnosis, and make sure we’re supporting those affected by breast cancer in every way that we can.
As a genetic counselor who has worked in cancer centers, here are some of the questions I got from my patients most often.
Q: I was recently diagnosed with breast cancer, and I can’t tell all the genetic tests apart. What’s the difference?
There are two main types of genetic tests for people who have been diagnosed with breast cancer:
- Germline tests look at the DNA that we are born with. This is the same genetic code that’s in almost every cell in our body. Most germline tests are typically done using DNA isolated from a blood or saliva sample. This is also mostly the DNA that we inherited from our parents, and that we pass onto our children. Germline tests are often trying to help a person determine if they are at an increased odds of developing certain types of cancer over that of the general population, but sometimes can also play a role in the type of surgery or chemotherapy a person chooses in the event that they develop cancer. The well-known BRCA genes are tested in germline tests, along with many others.
- Somatic tests are a form of DNA testing, but rather than looking at blood or saliva, they look at the DNA in other types of tissues that may not represent the DNA you inherited. In the context of cancer, it refers to DNA in tumor cells.
The somatic test that happens for almost anyone diagnosed with breast cancer is called the Her2/neu test. This is done on DNA taken from a tumor biopsy, or sometimes from a part of the tumor removed during surgery, but it’s always looking at the DNA within the tumor. This test can help the oncologist determine how the tumor will react to different medications. A similar test that is becoming more common is known as tumor genome sequencing. Instead of the Her2/neu test, which looks at just one area of the tumor’s DNA, tumor genome sequencing looks at hundreds or thousands of genes. The focus of this test is to find the primary driving factor(s) that is causing these cells to become cancerous.
Identifying these “driver” variants in the tumor DNA helps oncologists determine which chemotherapy to use; if they have a drug that targets the driver, they’re likely to use it. In some cases, the results from tumor genome sequencing will also indicate whether a person qualifies for a clinical trial. Typically in these cases, the clinical trial is specifically designed for people who have particular gene variants in the tumor’s DNA.
Q: Besides BRCA, are there other genes associated with cancer predisposition?
Yes. The BRCA (BReast CAncer) genes are not the only genes that affect the risk of breast cancer, and there are genes that can affect the likelihood of developing cancer in other organs as well. Researchers have identified dozens of other genes that can affect a person’s odds; CDH1, PTEN, P53, ATM, and CHEK2 are just some examples.
As our understanding of cancer improves, so too do our screening methods. Many germline panels now test for variants in these genes as well as a number of others. There are many differences between the genes including how likely the gene is to affect someone. For example, one gene may raise a person’s lifetime risk of breast cancer to somewhere in the neighborhood of 50% (that’s a 1 in 2 chance), but another raises it to about 20% (a 1 in 5 chance).
Q: If the genetic testing does find something, can I do anything about it?
Germline genetic testing has played a huge role in prevention, to the point where people who have tested positive for a variant and taken preventive action have created a new word for themselves : “previvors.” Here are some of the primary steps people can take if they have a variant in a breast cancer predisposition gene, like one of the BRCA genes:
- Men and women are advised to be sure they know how to do a thorough breast-self exam, do them monthly, and inform their doctors of their genetic test results.
- Women can also screen more regularly with mammograms and breast MRIs (some men may choose to do these as well).
- Additionally, women can be prescribed a medication which affects how estrogen works in the body to lower the odds of breast cancer.
- Other avenues include preventative mastectomy, in which breast tissue is surgically removed, with the option to have reconstructive surgery following the mastectomy.
Q: If I’ve tested positive for a cancer predisposing variant, does my family need to be tested?
Once someone tests positive for a variant, it’s important that they tell their relatives so they have the opportunity to get tested and see if they inherited the same variant. That could help them screen, prevent, or possibly even treat a future cancer.
The BRCA genes, as well as most germline cancer predisposition genes, are inherited as autosomal dominants. “Autosomal” refers to genes that can come from mom or dad and be passed onto sons or daughters. “Dominant” means that it only takes one copy of the variant for a person to develop the disease or have the predisposition. Since parents can only pass on half their genetic material to their kids, it’s a 50/50 chance that a man or woman who has a variant in a cancer predisposition gene will pass it on to their child. And the gender of the child also doesn’t matter. (For parents considering having their children tested, note that most of the time testing is recommended after age 18.)
Q: If I’ve had genetic testing before and nothing was found, do I need any more testing?
Maybe. It’s important to understand that genetics is still a relatively new science, and new genes that affect cancer predisposition are still being discovered. So although testing negative for a particular set of gene variants lowers the odds that there’s something genetic or hereditary in play, it doesn’t eliminate the possibility altogether. If you’ve had testing over the past few years, you might consider checking in with the doctor or genetic counselor who ordered your test to see if update testing is right for you.
Most people who have genetic testing for cancer predisposition test negative, and it’s often a relief. Other times, though, people have mixed feelings because they were hoping to solve a mystery, like why they developed cancer in the first place, or why many of their relatives have had it. These are normal emotions, and can sometimes be a sign that grief counseling is worth pursuing.
Q: If I’ve tested negative, does anyone in my family need to be tested?
Maybe. It really depends on your personal and family history. When a person tests negative, it’s still possible that other relatives could test positive because of the 50/50 odds of passing a gene with a variant. So if you tested negative, it might be the case that other relatives carry a variant in a gene like BRCA, but you just didn’t inherit it. For this reason, it’s often the most efficient to test the person who had the cancer diagnosis, if they are available and interested. If there are multiple people in the family who have had cancer, a genetic counselor can help you determine who the best person in the family to test is.
Q: Are there other resources if I have more questions?
Yes! We’ve only scratched the surface here. A breast cancer diagnosis—or a positive test for a gene variant associated with breast cancer—can obviously raise many more questions than we have a chance to address in this one blog post. The National Cancer Institute’s website and www.genome.gov are good starting points with links to educational material, support resources, and information regarding clinical trials. FORCE and Bright Pink are support/advocacy groups. Genetic counselors are also available and often covered by insurance with a referral from your doctor; Helix has partnered with Genome Medical for genetic counseling services, and more information can be found here.
Helix is the leading population genomics and viral surveillance company operating at the intersection of clinical care, research, and data analytics.