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The Genetics of Breast Cancer

Dr. Susan Miesfeldt, MD

Featured Speaker

Susan Miesfeldt, MD

About 5% to 10% of breast cancers are thought to be hereditary, caused by abnormal genes passed from parent to child.

Most inherited cases of breast cancer are associated with two abnormal genes: BRCA1 and BRCA2; however, there are other genes associated with breast cancer risk. Getting tested for the mutations of these genes is a very personal and private decision women must make with their doctors. They can then decide with their physicians what to do with that information. 

Listen in as Susan Miesfeldt, MD discusses The Genetics of Breast Cancer.

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Melanie Cole (Host): About 5-10% of breast cancers are thought to be hereditary, caused by abnormal genes passed from parent to child. Most inherited cases of breast cancer are associated with two abnormal genes, the BRCA1 and the BRCA2. My guest today is Dr. Susan Miesfeldt. She’s the Director at the Center for Cancer Risk and Prevention Program at Maine Medical Center. Welcome to the show, Dr. Miesfeldt. What’s the link between breast cancer and genetics?

Dr. Susan Miesfeldt (Guest): It’s important to note that all cancer is related to genetic defects but the majority of cancer is due to genetic defects just within the cancer cells. About 10% of cancers, you noted, is related inherited genetic defects. These are errors in genes that we all have that we may inherit from either parent and when we do inherit these genetic abnormalities, it makes us at much higher risk of developing cancer and causes us to be at increased risk for specific types of cancers. Relative to hereditary breast cancer, the two most common high-risk breast cancer related genes are BRCA1 and BRCA2.

Melanie: So, does everybody have these genes?

Dr. Miesfeldt: Yes. Everybody has two copies of both the BRCA1 and the BRCA2 genes. These are normal genes that help our cells to stay healthy. And when, again, we inherit the abnormal copy of either of these genes from either of our parents, that’s when the disease susceptibility becomes an issue. 

Melanie: So, it’s a mutation of these genes that is inherited. How would we know, Dr. Miesfeldt?

Dr. Miesfeldt: Well, you know through genetic testing but not everyone’s a candidate for genetic testing. The folks we see in clinic who we do advise genetic testing in, are individuals with certain personal or family history characteristics. Those general characteristics are, for the individual, any diagnosis of ovarian cancer, that’s enough of a risk factor that can consider BRCA1 and BRCA2 testing. But, other risk factors are development of breast cancer at a younger than expected age. So, most breast cancer happens well after menopause. So, when we start seeing women with breast cancer less than the age of 50, those women are oftentimes candidates for genetic testing. Other family history factors that we look for are, obviously, if you’ve got a strong family history of multiple relatives with breast cancer or if there are any male breast cancer cases in your family, that’s another criteria for genetic testing. And then, finally, what we look for are specific patterns within the family of cancers that tend to track together and are associated with specific genetic mutations. For example, if there’s a family with breast and ovarian cancer within multiple relatives, that’s the family that we want to see, and consider testing in.

Melanie: Are there other things that put us more at risk like certain hereditary factors?

Dr. Miesfeldt: Well, BRCA1 and BRCA2 are two hereditary factors, but there are other genes that are linked to breast cancer risk. It’s important to recognize that. When we do genetic testing in families, the most common genetic markers that we find are the BRCA1 and BRCA2 genes, but there are other genes that are very tightly linked with breast cancer, so oftentimes nowadays when we do breast cancer related genetic testing, we may be looking at 12-17 individual genes, two of which are the BRCA1 and BRCA2 genes but, again, there are others that we would analyze as well.

Melanie: Are there certain segments of the population that would be considered more at risk?

Dr. Miesfeldt: Well, those with breast cancer especially when looking at the factors that I just mentioned, but the other population that we look for are male breast cancer cases because that is a risk factor for mutations, especially in the BRCA2 gene. The other population that has been studied nationally is the Ashkenazi Jewish population. So, individuals of Ashkenazi Jewish heritage do have an added risk for BRCA1 and BRCA2 mutations. However, we don’t test every individual of Ashkenazi Jewish Heritage. We look for families with breast cancer or ovarian cancer to determine testing.

Melanie: So, what’s involved in the testing?

Dr. Miesfeldt: It’s a blood test, so it’s pretty straightforward. It’s not done in individual institutions. There are large genetic testing labs throughout the United States. So, any center doing genetic testing uses these national labs. But, it’s a blood test that’s submitted to these labs that usually takes anywhere from three to five weeks to get a result back. These results are typically given to the individual and family in person and all of this is done within the context of genetic counseling so that the individual and family understands the implications of genetic testing.

Melanie: Then what? How long do they wait for the results and what do they do with them?

Dr. Miesfeldt: So, it depends on the testing lab we use, and it depends on how many genes we’re analyzing, but the typical turnaround time, the time between when we order the test and when we disclose the results, is usually three to five weeks. When a result comes back, we expect one of three findings. Most often because these are pretty rare genetic conditions, we expect a negative, which means the lab is unable to find a mutation or an error in one of these genes. Second is, they do find an error that they think is the cause of increased cancer risks. That’s obviously called a “positive” and direct care and I’ll get into that a little bit more. The third result is, we all have minor variations when we compare our different genes and, so, occasionally the lab will find a change in a gene but they don’t know if it’s just natural variation or it’s disease risk causing. It’s called “a variant of uncertain significance”. We can't use that result to guide care. We just follow that with time and, ultimately, the lab gives us more information on those specific variants. So, when we get a positive result back for an individual, it means that that individual has the genetic condition linked with the mutation of that specific gene. So, for example, an individual with a BRCA mutation has a condition called “hereditary breast and ovarian cancer syndrome” and this primarily affects women but it affects men as well. So, for women, they’re facing significant risk for breast cancer and significant risk for ovarian cancer, so we guide these women into high-risk screening services and many of them think about preventative surgery, especially preventative removal of the ovaries and fallopian tubes. And even men, they do face elevated risk when they have these genetic mutations, so we steer men to appropriate services as well. Obviously, the other implications of genetic is to others in the family, so we are very careful to instruct individuals getting positive results to alert their families so that they can seek appropriate genetic counseling and testing and respite care.

Melanie: Now, in the media, people have heard about prophylactic mastectomies or hormone therapies that you can then go on if you do test positive. How do you counsel women about this particular test and what they should do with these results?

Dr. Miesfeldt: Well, any women with a BRCA mutation, obviously, women who don’t have other medical issues, are offered a number of different options. In terms of breast cancer, a woman chooses between aggressive surveillance, namely being followed very carefully on a six month basis through clinical exams and then, alternating mammograms and MRIs of the breast to follow the breasts very carefully because, again, these women are facing significant risk for breast cancer. Neither of those screening tools--mammograms and MRIs--don’t lower the risk of getting breast cancer, they’re just aimed at picking it up as early as possible. Some women do want to reduce their risk and we counsel women pretty aggressively in terms of lifestyle factors that are known to be associated with cancer risks. But, these women with BRCA mutations are also offered things like chemo-prevention, which is use of anti-estrogen drugs to lower breast cancer risk. So, we will talk to women about the options of these anti-estrogen drugs. And then, some women, because they’re facing upwards of a 50% chance of breast cancer, do decide to have bilateral mastectomies done in a risk-reducing setting so that they lower their risk of getting breast cancer. So, all three of those options are addressed with women when they get a positive BRCA result back.

Melanie: If they test positive for these mutations, can they be discriminated against? Does this go on their medical record?

Dr. Miesfeldt: It certainly goes in their medical record because it directs their care. In terms of discrimination, there’s very strong legislation, both at the state level within Maine, as well as at the national level to protect all of us against health insurance discrimination based on genetics. We sometimes have concerns about things like disability insurance or life insurance but these don’t tend to be major issues and, quite honestly, the greatest issue was related to health insurance discrimination, and, again, we’re all protected against that.

Melanie: So, give us those lifestyle modifications. Tell us what you really want us to know about preventing breast cancer, keeping an eye out for symptoms, red flags, and the genetics of breast cancer.

Dr. Miesfeldt: In terms of cancer in general, there has been a lot of recent data in terms of how lifestyle impacts risk for all cancer. The top four lifestyle habits that have been pretty strongly linked with all cancer risks are avoiding tobacco products--that’s the most important lifestyle factor that’s been linked to cancer nationally--but a pretty close second are three things together: lack of physical activity, poor nutrition and weight. Those three factors together are starting to catch up with tobacco as the number one cause of cancer, nationally. So, general rules of thumb that we always talk with all of our patients about are getting at least 150 minutes of aerobic exercise a week and things like walking or cycling or swimming are good forms of aerobic exercise. Nutrition. The most important nutrition to find off cancer risk is lots of fruits and vegetables, at least five servings a day. And then, in terms of weight, we should all know what’s called our “body mass index” which is a reflection of our height and weight. This is something, generally, that our primary care physician tracks. I you don’t know your BMI, you should ask your physician what your BMI is or there are ways that you can calculate it online. So, this is an important number to know because it is pretty strongly linked to cancer risk, including breast cancer risk. We all want to have a body mass index between 19 and 25. So, those are some general rules of thumb in terms of overall health, cancer risk in general and breast cancer specific risk. The other important issue with breast cancer is it’s been linked to hormone replacement therapies, so that’s something we address with women coming in for risk assessment and counseling is the influence of hormone replacement therapy on breast cancer. The final thing is, alcohol has been linked to breast cancer risk as well, so we generally recommend that women drink no more than an alcoholic beverage a day and less is probably better. 

Melanie: In just the last minute here, please tell us about the Center for Cancer Risk and Prevention Program at Maine Medical Center.

Dr. Miesfeldt: We are a multidisciplinary program within the Maine Medical Center Cancer Institute. We’re staffed by professionals who assess families at potential risk for hereditary cancer susceptibility. We have three skilled genetic counselors working in the clinic as well as two physicians that guide the families that come to us. These are families that are at risk for hereditary cancers susceptibilities. So, we go through their histories, we determine their risk, we assist them in deciding whether or not to pursue genetic testing and then guide their care based on the genetic test result. We are within the Scarborough Campus at Maine Medical Center. Our contact information is on the Maine Medical Center webpage. 

Melanie: Thank you so much for being with us. It’s great information and so important for women to hear. You’re listening to MMC Radio. For more information, you can go to That’s This is Melanie Cole. Thanks so much for listening.