Dense breasts reduce the effectiveness of mammograms and increase the risk for breast cancer. Dr. Sally Herschorn explains why, and talks about a new law that will help women find out if they are in this category. Learn more about breast density.


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UVM Medical Center: Mammograms of course are one of the most important preventive screenings women can have because they can detect potentially cancerous growths much earlier than those growths could be felt, but for 40 to 50% of women who have dense breasts, it’s more difficult to spot those growths because the image contains more white in it than would be the case for mammograms in women with non-dense breasts, and white is also the color of the growths that radiologists are trying to find. In fact dense breasts are the most common reason for missing cancer on a mammogram.

So what can be done to overcome this problem? Well we’re going to find out on today’s program and also learn about a new Vermont law that’s designed to make it easier for women to find out if they have dense breasts. Our guide is Dr. Sally Herschorn, a radiologist and Medical Director of the Breast Imaging Division at the University of Vermont Medical Center, also an Associate Professor at the Larner College of Medicine and Vice Chair of the Patient and Provider Experience in Radiology.

Dr. Herschorn and her colleagues have put together a really thorough and wonderful website that gives you time information about breast density and here’s how you find it. You go to, so that’s the main website for UVM Medical Center and you just find the search box right at the top on the right and you put in dense breasts it’ll bring you right to that page. Thank you for coming.

Dr. Herschorn: Thank you for having me.

UVM Medical Center: So let’s start with basics about mammograms and what you guys see. I mean most of these still are two dimensional images, right?

Dr. Herschorn: Actually in our practice we are doing primarily three dimensional mammograms for screening. We’re here 85 to 90%.

UVM Medical Center: Wow! That’s great. So you’re looking at just people in your state and you’re looking at this computer screen and what can you do with that image and how does it help you, this new technology find what you’re looking for?

Dr. Herschorn: So cancers can often be masked on a mammogram by overlying breast tissue and having a three dimensional mammogram you can page through similar to paging through the pages in a book and see each page separately instead of everything superimposed on each other. Studies have shown that you can detect more cancers with 3D mammography as well; there are fewer things that might look like cancer that might cause you to call the patient back when they aren’t real.

UVM Medical Center: So, and I’ve seen you do this before, you’re sort of pushing slowly through this image and all of a sudden you will see the next very, very thin layer and all of sudden you can say, “Oh, there’s something new.”

Dr. Herschorn: Exactly.

UVM Medical Center: There’s something worth looking at there.

Dr. Herschorn: Exactly. In a two dimensional mammogram everything from the top to the bottom is superimposed one over the other and things can be obscured or images can be created that aren’t really there. When you use 3D that really helps a lot.

UVM Medical Center: Now this technology allows you to see a lot more and does that prevent the problem that you notice a lot more and so you really have to be on top of your game to be able to tell whether it is something that is concerning or not?

Dr. Herschorn: Well that’s true. You really have to be skilled and experienced and it also takes the radiologists a lot more time to look at these images. It’s a lot more tedious as you might call it to page through 40 or so images per breast instead of two images per breast. It really is a difficult process. Despite that, radiologists are uniformly completely in favor of doing this because the results have been so spectacular.

Let me put it another way for you. Screening mammography the two dimensional way has always been good or moderately good. You can add things to it to supplement your cancer detection but anything that you add to it is going to have its own set of false positives, so anything you add is going to have a disadvantage. There’s no free lunch in the world, right? But if you substitute three dimensional mammography for two dimensional mammography, you will both increase your cancer detection and decrease your false positives. It’s the only technique that we’ve ever had that gives you the good of one and decreases the bad of the other. That’s why we’re so excited about it.

UVM Medical Center: That’s fantastic. You have this dense breast tissue. First of all explain what that is and then we’ll talk about what it looks like to you.

Dr. Herschorn: Breast density refers to the appearance of the breast tissue on the mammogram and the normal breast is composed of a mixture of fibrous glandular and fatty tissue, and the fatty tissue allows the x-ray beam to pass through so it appears dark on the image. The fibrous and glandular tissue are both similar in density and they allow less of the x-ray beam to pass through so the image appears white on the mammogram. The importance of that is the masking effect.

As you said in the beginning, when there’s a lot of dense breast tissue where the image is white, it’s much harder to spot cancers which usually appear as white. The more tissue there is, the more masking, the more difficult it is to pick up cancers. The number one reason for missing a breast cancer for mammography is dense breast tissue, so with dense breast tissue it’s important for women to know that their mammogram is not as good. In women who have primarily fatty breasts, the mammogram is 98% accurate in picking up breast cancer, but in higher breast densities, it can be less than 50% effective. It really is a big difference.

In addition to being less effective at picking up cancers, women with dense breast tissue are also at higher risk for breast cancer than the average woman so it’s important for women to know that. The higher the breast density, the higher the risk. Now there’s a lot of reasons for having an increased risk in breast cancer. Things like a genetic mutation like a BRCA1 or 2 mutation would greatly increase a woman’s risk of having breast cancer. Things like having a family history such as a mother or sister or daughter with breast cancer moderately increase a woman’s chances of having breast cancer during her lifetime by 1.5 to 2 times and that’s about the order of magnitude that breast destiny adds to the risk. It’s not the super high risk that genetic mutations add but it’s a moderate increase in risk.

UVM Medical Center: So this is really an important issue.

Dr. Herschorn: It’s an important issue because one size doesn’t fit all and screening women, all women with the same tools works better for some women than for others. You know, we’ve known for a very long time that mammography is not very good at detecting breast cancer in women with dense breasts and radiologists since the early ’90s have always reported the breast density to the patient’s physician so that in the report the physician would know how reliable is that mammogram at picking up breast cancer if it’s there.

Physicians have not always discussed this with women and some women have asked about it but not everybody does and not everybody’s aware of it. So there’s a big patient activism and engagement movement and this stems from women with dense breasts who got diagnosed with advanced cancers in a later stage and wanted other women to benefit and not be subject to what happened to me.

UVM Medical Center: You’re telling me about one woman in particular who really got the ball rolling.

Dr. Herschorn: Nancy Cappello, Dr. Nancy Cappello was an educator in Connecticut, a PhD in education who worked for the Department of Education. She was healthy. She did everything for her health, got regular physical exams with her doctor, had mammograms every year, kept a healthy weight, exercised regularly, ate healthy, and then she felt a lump about two or three weeks after her 11th normal mammogram and it turned that she had quite an advanced breast cancer Stage 3 with 13 positive nodes.

She required a mastectomy and chemotherapy, and after going through all that, she went to her doctor and she said, “Why did this happen? I did everything I was supposed to? How did I not get diagnosed early?” Her doctor said, “Nancy, you have dense breast tissue.” Nancy said, “You knew? Why didn’t I know? What does that mean? Why wasn’t I informed? I might have wanted to do something else in order to prevent this late stage diagnosis?”

That was, the treatment was obviously very, very difficult for her. So after she recovered she went to work trying to get this information to be available to women. She created a website called and she got followers from all over the world to submit their stories. They all had similar stories. Eventually she got enough funding and political activism to get the Connecticut State Legislature to pass a law requiring radiologists to release this information to patients. That was in 2009, the first mandatory breast density notification legislation in the country.

Since then, 28 states have passed legislation. Vermont is the latest. We passed our legislation in May and it goes into effect January 15th.

UVM Medical Center: I just want to interrupt for a second to tell you you’re listening to Dr. Sally Herschorn. She’s a radiologist and Medical Director of the Breast Imaging Division at the University of Vermont Medical Center, also an Associate Professor at the Larner College of Medicine and Vice Chair of the Patient and Provider Experience in Radiology.

What would a woman do with this information when she gets it?

Dr. Herschorn: There are a lot of other options available to women to increase cancer detection. The first one is 3D imaging or tomosynthesis as we discussed earlier. It increases the cancer detection. That may be enough for some women. For those with extremely dense breast and for those at higher risk, the studies show that it still may not be enough so those women may want to add tests such as ultrasound screening or MRI screening.

As far as who should get what, in general, women who are at very high lifetime risk for breast cancer, 20% or more, regardless of whether they’re dense or not, should supplement their mammogram with MRI. For those who are less than 20%, then it’s a choice and it’s what’s available and what their insurance may want to pay for. There are only five states by the way that mandate that insurance pay for these additional testing. Vermont is not one of them.

UVM Medical Center: So are there any disadvantages to additional screening?

Dr. Herschorn: Well sure. The disadvantage of adding anything except 3D mammography is that you have more false positives and that involves coming back. That involves anxiety. That involves cost, and it’s not for everybody. That’s why because there are no firm guidelines, it’s a personal decision about values. I might be a woman who says like Nancy, “I want to do everything I can so that if I get breast cancer, it’s going to be diagnosed early and I’m willing to put up with false positives. I’m willing to put up with a biopsy for the chance that if I can get diagnosed early and I don’t have to undergo chemotherapy, that’s my goal.”

Fine, then that person should have additional testing and she can decide with her doctor what the best kind is for her and it may be different in different years. But for someone else who says, “I really don’t like the idea of too much testing and too much false positive,” you know that woman may be perfectly fine to just follow screening mammography and not do anything else.

We’re not trying to force anybody into testing and if we had firm medical guidelines that conclusively showed that deaths were prevented by doing this additional testing, we would recommend that. Those studies have not been done yet and I don’t think they will be done because the screening mammography studies that show conclusively that deaths are prevented by doing screening mammograms were done many years ago. They were very expensive. No one has the time or money or infrastructure to repeat those studies. Even though they showed conclusively, we’re still arguing about that years and years later.

What we’re going to have to do with these other additional testings is not use death as an endpoint. We’re going to have to use stage of cancer diagnosis as a substitute for that endpoint, and it doesn’t really have the conclusive proof that using death as an endpoint does.

UVM Medical Center: I’m listening to all of this and thinking, you know, there are a lot of options, a lot of decisions for women to make and so more information like knowing that you have dense breasts is really important. You can initiate that conversation with your primary care physician and then as you go down the line.

Dr. Herschorn: Yeah, it certainly is important for women to know about it, initiate the conversation with their primary care and use it as an opportunity to discuss risk and screening and values, and how you want to be screened and how you want your risk to be handled.

UVM Medical Center: All right, I’m afraid we’re going to have to leave it there, but I want to thank my guest, Dr. Sally Herschorn, a radiologist and Medical Director of the Breast Imaging Division at the University of Vermont Medical Center. She’s also an Associate Professor at the Larner College of Medicine and Vice Chair of the Patient and Provider Experience in Radiology.

Dr. Herschorn and her colleagues have put together a really thorough and wonderful website that gives you a ton of information about breast density and here’s how you find it. You go to, so that’s the main website for the UVM Medical Center and you just find the search box right at the top on the right and you put in dense breasts. It’ll bring you right to that page.

Thanks very much for being here.

Dr. Herschorn:  Thank you.


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