By now, you’ve probably heard the call to Know Your Breast Density!  You may have even seen articles about women who are angry because their doctors never told them they have dense breasts or who believe that if they had known they had dense breasts their cancer would have been detected earlier. You may have even applauded new legislation that tells doctors they must inform women about their breast density. But the latest research suggests that it might not be the densest breast tissue we need to be most worried about.

Understanding Density
The breast contains ducts, glands, fibrous connective tissue, and fatty tissue. A breast that is considered dense has more fibrous, connective tissue and less fatty tissue, while a very low density breast contain almost all fatty tissue. Virtually all women start out with very dense breast tissue. Over time this changes, and, as a woman ages, her breasts typically become more fatty and less dense. However, there are some women whose breasts remain dense, even after menopause. And there are others whose breasts become completely fatty.

Breast density can only be determined by looking at a mammogram of a woman’s breasts. (A system called BI-RADS is used to report density, which is ranked from 1 (least dense) to 4 (most dense)). For decades, we thought that the problem with dense breasts was that they made it more difficult to detect a tumor: Both dense breast tissue and a tumor appear white on a mammogram, which makes finding akin to looking for a polar bear in the snow. This is one reason why mammography does not find all breast tumors. It is also one of the reasons why mammography is not a very effective screening tool for young women, who typically have dense breasts.

More Than White Tissue
Five years ago, we wrote about a study published in the New England Journal of Medicine that found that breast density was an independent risk factor for breast cancer in women who are close to 50 or who are postmenopausal. This study changed the way we thought about dense breast tissue, because it meant the problem wasn’t just that these tumors were harder to detect.

This study also led some breast cancer advocates to begin promoting the need for women to learn their breast density. This, in turn, led to calls for legislation that would require doctors to tell women their breast density. Four states have already passed this legislation, and more than a dozen other states have bills that could be approved.

But the talk about dense breast tissue often left out some important facts. For example: having dense breasts at 40 is quite normal. The risk increases if your breasts stay dense as you grow older, and after menopause. It also sometimes gave the impression that the only tumors not found on mammography and diagnosed at a later stage were those in dense breast tissue. But that’s not the case. Studies show that about 38 percent of breast cancers are diagnosed at a late stage, but this is not solely due to dense breast tissue. It’s because the tumor’s biology is aggressive.

Why Density Matters
Our need to rethink what we know about breast density again highlighted by findings from a recent study on mammographic density that surprised many by showing that women with dense breast tissue are, in fact, not more likely to die of breast cancer.

This study published in the Journal of the National Cancer Institute looked at 9,232 women who had been diagnosed with breast cancer between 1996 and 2005. About 84 percent of the women were classified as BI-RADS 2 or 3. (Specifically, 560 were BI-RADS 1; 3735 were BI-RADS 2; 4019 were BI-RADS 3 and 918 were BI-RADS 4.)

The researchers followed the women for six years after their diagnosis. During that time, there were 1795 deaths 889 from breast cancer and 810 from other causes. When all breast cancer stages were combined, there was no relationship between BI-RADS density and breast cancer death. However, among women whose tumors were 2.0 cm or more, BI-RADS 1 density was associated with an increased risk of breast cancer death. And, importantly, BI-RADS 1 density the most fatty breast tissue was also linked to obesity.

Tumor Biology Matters
Could it be that dense tissue represents a local microenvironment that promotes cancer development, but not spread? Or that the low breast density seen in obese women creates a microenvironment that makes tumors more aggressive? That is something we need to study. Tumor biology might also explain why the risk factors for developing breast cancer may not necessarily be the same as the factors that influence a woman’s risk of dying from breast cancer. In other words, maybe dense breast tissue increases the risk of getting cancer, but not dying of it. If this is true, it might mean we don’t need to treat the tumors of all women with dense breast tissue the same way, or the same as we would a woman with fatty breasts.

It’s especially important to think about these findings in the context of the mammography debates and the push for breast density legislation. All too often, a recommendation like the one the US Preventive Services Task Force made for routine mammography screening to begin at age 50 is interpreted as a conspiracy to cut health care costs that will ultimately increase breast cancer deaths. Or, we look to legislation, like the laws we’ve seen about breast density, as a way to get women more screening even though there is no evidence that more screening is better.

We have repeatedly bumped up against the limits of what screening can do. We need to focus more on the tumor’s biology and the microenvironment that surrounds it, it we are going to end this disease. The recent study on breast density showed us, yet again, that women who are obese when they are diagnosed with breast cancer are more likely to die of breast cancer than women who are not obese. Doctors need to do more than tell women about their breast density or remind them to get a mammogram. They need to be teaching women the importance of exercising, losing weight (if necessary) and eating a well-balanced diet both before and after a breast cancer diagnosis.

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18 Responses to Breast Density: What We Know May Surprise You

  1. Jonathan says:

    Very interesting. I always wondered about this since postmenopausal obsesity is such a pronounced risk factor even though breast tissue in these women is fattier.

    It also makes me wonder about why tamoxifen can decrease breast density so quickly and that aromatase inhibitors do not, even though AIs are more effective at treating cancers, preventing recurrences, and reducing the risk of primary breast cancer in high risk women. May also explain th paradox of tall, slender premenopausal women having a higher risk, which then does an about face after menopause, with heavier women being more at risk.

    Hope you’re doing well Dr. Love!

  2. Nanci says:

    As a woman of 62 who has dense breast tissue and who has only had 3 mammograms in her life (age 40, age 51 and age 61), this is heartening news. My breasts were so dense that when I got the reading that said they were too dense to be able to tell anything (first 2 mammograms) I refused to irradiated yearly only to be told “can’t see, breast tissue too dense.” Last year was the first digital and finally, a clear and clean diagnosis. I do keep my weight down, just squeaking in on the normal weight range at this stage of my life, I exercise daily for my heart and to keep my muscles supporting a bad knee, strong, and I moved to a mostly vegan, little bit vegetarian, fish once a week diet last year to avoid a statin (and boy did THAT lower my levels, plus I feel great, wish I had done this sooner, just more effort in cooking). It’s a lot of effort, this aging in as healthy a manner as possible, but I have friends on both sides of taking care of themselves and the ones who have and do are faring so much better, I grumble and then hit the mat and treadmill (and walk outside as much as possible!), and only choose to eat one sweet thing a day instead of the five or six that I would like, smile. I hope that you’re doing well Dr. Love. Your books and writings have been touchstones for me.

  3. I had both breasts removed when I was diagnosed with stage 4 breast cancer in 2005, so I have no idea where my dense breasts fell on the density spectrum. All I do know is, every woman I met during treatment who was diagnosed stage 4, had tumors that never showed up on a mammogram. Mine, included. The point to me is, women with dense breasts should NOT get mammograms. They should get MRIs, or ultrasounds. At the time of my diagnosis, the tumor showed up clearly on an ultrasound. Of course this means that all the financial investment in the mammography model would have to be dumped, and we can’t have THAT, can we. So what if lives are on the line. The talking heads can parse this issue any way they want, but it always boils down to the same thing. Your responsibility is to ask your doctor if you have dense breasts. If the answer is “yes”, then even if you have to pay for it outside your insurance, get an MRI or ultrasound. We have to save our own lives, because sometimes the money issue is stacked against us.

  4. Susan Sickler says:

    I found out the hard way that faithful yearly mammograms are not the safety net that we like to think that they are. There is a big hole in our preventive teaching. When you notice changes in the look of the breast such as dimpling or nipple retraction the person to see first is either your primary care physician or your GYN for a clinical breast exam. DO NOT get a routine mammogram and if is is negative assume that all is well. These are signs of lobular carcinoma and it rarely shows up on either a mammogram or ultrasound. Insisting on a MRI if the other tests are negative may save your life and the primary care physician is in the best position to fight for your chance to have the MRI. Lobular will frequently not present with a lump that you can feel either so it can get quite large before it is diagnosed unless someone has the clinical experience to tell from the look of the breast that further testing is needed.

  5. I agree about dense breasts! I was never given an option for MRI or ultrasound even though I have dense breasts. Once I had breast cancer my options were limited!

  6. I agree about dense breasts! I was never given an option for MRI or ultrasound even though I have dense breasts. Once I had breast cancer my options were limited! Never saw anything on any of my yearly mammograms from 21 to 51! Wish I never had any mammogram! Doctors didn’t give me the right information and I didn’t ask the right questions! Hope others will learn from this…

  7. Barbara J says:

    Dense breasts — yes. Both gone now. 41 years of mammography since 18 and first benign tumor. Then mamograms and ultrasound for the last 15 years. Cancer only then truly identified on MRI.
    Should have, could have, demanded it earlier? Tried. Breast removal at 25 and then age 42 was recommended due to density.Happened at 59 with diagnosis. But could have just had MRIs. Profit and insurance companies should no longer be guiding forces in women’s health! Speak up!!

  8. Mona V. says:

    Since BC is really at least 4 separate diseases, the implications of BI-RADS score on breast cancer incidence or mortality is much more complex than these studies can really demonstrate. Studies would actually need to separate out the different genotypes and determine which ones are associated with which breast morphology, and which findings on mammogram with those specific types of BC portend a worse prognosis. When studies mush all the types of breast cancer together, it creates a murky view of possible associations.

  9. Nan says:

    Know your breast density. Get an MRI if any ? of unclear mammogram, even if it is on your dime$$$. Insurance Co. better start paying for this in appropriate situations,as this can be a lifesaver,and a $$$ saver in the long run. We must keep pushing for the BEST care. I hope your doing very well, Dr.Love. Let us know when you can. You are in my prayers.

  10. Lois says:

    I had dense breasts. One tumor was identified on a mammogram because the radiologist noticed the change from the one the year before. Ultrasound and MRI did NOT identify any additional tumors in either breast. Following a lumpectomy, pathology uncovered additional tumors. I elected to have a bilateral mastectomy. Final count was 15 tumors in one breast and a DCIS in the other, many of them large enough that they should have been seen. Even now knowing where the tumors were located, the radiologist could not find them on the scans.

    MRI may be a good alternative, but it also is not 100%.

  11. There is indeed evidence that more screening is effective in women with dense breasts. In 2009, Connecticut became the first state to enact a Breast Density Inform law. A follow-up study about to be published was conducted by Drs. Sarah Steenbergen and Jean Weigert after a full year of the law’s enactment. The analysis involved clinical data from over 78,000 women. Findings? For dense breasted women – who had no other risk factors – the addition of a screening ultrasound after mammography DOUBLED the number of cancers found by mammography alone.

    Further, as women with dense breasts are at greater risk of developing breast cancer, their risk of dying from breast cancer is elevated compared to the general population. While a dense breasted woman diagnosed at Stage IV may have the same risk of dying as a woman with fatty breasts diagnosed at Stage IV, research indicates that women with extremely dense breasts are 4 to 6 times more likely to develop breast cancer and could therefore be 4 to 6 times more likely to be Stage IV than women with fatty breasts,
    Five states now require Breast Density disclosure to women and Federal Bill HR3102 has been introduced.
    For further information about Breast Density and legislation to get this lifesaving information to women, please visit: ww.AYDadvocacy.org

  12. Lisa says:

    I have a very small palpable lump that did not show up on mammogram or ultrasound, although many other cysts did show up. To be safe, I was sent for an MRI. The results are as follows:

    “Scattered fibroglandular densities are noted. Innumerable varying sized cysts are present throughout both breasts, probably indicating underlying fibrocystic condition.

    There is a glandular background element enhancement which does limit assessment; however, no suspicious area of enhancement is seen at this time.”

    “No suspicious” sounds good to me, but should I be worried about “glandular background element which does limit assessment?”

  13. Mary Grace says:

    Whether it is the micro environment or not, that feeds the cancer, dense breasts are a big problem. I have had two primary breast cancers in each breast, years apart. First cancer mammo and ultra sound never saw the 2.3 cm tumor. You could see it sticking out the side of my breast but because the mammo didn’t see the tumor there was no tumor according to them. The second breast tumor was NOT seen either on the mammo, and I did not have a lump, the tumour was located inside near my chest wall. I had a pain there, that I thought was caused by working in the garden. The very smart nurse took an ultra sound and could see a very nasty looking area. So now I pay for my own MRI every year. The insurance will not cover me for an MRI. Two breast cancers did not show up on a mammo and only one with an ultra sound, and there is no help for me when it comes to MRI. Know your body and take care of it yourself.

  14. p!nk says:

    Thanks a ton for being my teacher on this topic. I actually enjoyed your current article greatly and most of all enjoyed reading the way you handled the issues I widely known as controversial. You happen to be always quite kind towards readers much like me and let me in my life. Thank you.

  15. CBMOM says:

    I am another mammogram breast density victim. Stage 3 Breast Cancer Diagnosis, 3″ slow growing tumor not seen on a mammogram for 3-5 years. Second 1″ tumor. I went every year to get my mammograms faithfully. I have lumpy breasts and got them examined by my OB/GYN annually. He even asked when giving me my breast exam about the lumpiness and questioned me to make sure that I was getting my mammograms. If my OB/GYN gives me the okay, I think that I am safe. Wrong! If the OB/GYN doesn’t understand the implications of dense breasts why would I? If I had known about the dense breast problem I would have been more diligent about the lumpiness in my breasts. Thank God California passed the law that requires that you are told about dense breasts. Unfortunately I was too late for me. To say that I am angry about this is an understatement. The radiology department that I went to has been deep in excuses and CYA ‘ing since my diagnosis. The radiologists have known better for along time and have not informed women about this. Unbelievable!

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  18. Tammy lou says:

    I’m 42 just had mammo n found out in full menopause just got email mammogram neg but have very very dense breasts o am at high risk for breast cancer wat should I do…..thanks in advance

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