What me worry

How to find out "mammographic density" and dense breast tissue

Further Reading

  1. Detailed cancer.org guide to breast cancer detection, including dense breast tissue” discussion.

Hints from a radiologist.

0% density   

You can ask for a copy of the radiologist’s report from your last mammograms. 

Sometimes the report will say whether or not the mammograms show dense breast tissue.  If the report says they are "very" dense,  then they are probably in 75% to 100% density category.  If the report says they are "somewhat" or "moderately" dense, then they are probably in the 50% to 74% category. If the report says the breasts are " entirely fatty",  they are probably in the 0% category.  If the report says they are "mostly" or "somewhat" or "partially" fatty, they are probably in the 1% to 24% category.    Note:  Some radiologists are not required to describe the mammographic density in their reports. Many radiologists do not mention anything about mammographic density, unless the density is great enough to interfere with their ability to interpret the mammograms.

What if the mammograms were taken as part of an organized screening program?

In this case, there may not be a written radiologists report,  but some screening result data must be recorded somewhere.  You can ask the screening program administrators if mammographic density is recorded in their databases.  Many (but not all) screening programs do this, and they may be able to tell you your mammographic density.

You can ask the radiologist

who reported the mammograms, to estimate your mammographic density percentage.  You can just ask “Do I have dense breast tissue?” Some radiologists would happily do this for you.  Others might be too busy or hard to reach.

You can ask to see your mammo films,

and judge for yourself.  Some mammography centers will loan you your mammograms.  Others may offer to charge you a fee to make copies of the films.  Without taking your mammograms away from the mammography center, should at least be able to look at them for free.  When you look at your mammograms you can judge the density for yourself. 
You shouldn’t worry too much making an inaccurate density measurement, because even radiologists have inter-observer agreement rates of about 0.75.  (I.e.  a radiologist estimating the density of a mammogram is likely to differ from the consensus of a group of radiologists about 25% of the time.) Its subjective.

See these examples of what mammograms look like

fatty breast
1% to 24% density
low density
25% to 49% density
50% to 74% density
moderate dense breast
75% to 100% density
dense breast tissue

A woman’s risk of breast cancer increases if her breasts are mammographically dense. You can test this using the breast cancer risk calculator.


Dr. Halls Dr. Halls
I originally made this page in year 2000, and updated the styling in 2014.

Megan Megan
Recently, some states in the USA made rules that require mammographic density to be reported on mammograms.

Dr. Halls Dr. Halls
I don’t agree with that. I think it’s bad to add verbage into mammo reports containing low-value information.

Megan Megan
Low value?, why?

Levi Levi
Suppose the report also said “she is tall, old and overweight”. Those are also risk factors and there’s nothing a woman can do to change them, or change her breast density.

Dr. Halls Dr. Halls
Organized mammographic screening programs and health insurance plans, don’t let women change their follow-up booking schedule based on those factors, so it’s wasted words.

Talking Moose
Talking Moose
And doctors skim reports too quickly.

Talking Moose
Talking Moose
Reminds me of a joke. I took a speed reading course and read War and Peace. It involves Russia.


The chat above is highlighting some risks,

  • The risk of doctors not noticing a report with cancer, because the report is outnumbered with useless words about breast density and birads numbers and which society or government set the guidelines, and so on.
  • The risk of having more people die due to annoyance and confusion about mammograms

Jessica Jessica
More people will die?

Holly Holly
What? Are you serious? What are you saying?


Here’s an example, from where I live, in the Province of Alberta, Canada. If a government sets a clear guideline that women should get mammograms ever 1 year, what happens? Women tend to come every 2 years. Some women develop a cancer during those 2 years, and some will die because of it. If a government sets a guideline that women under 50 can have mammograms annually, and rest can have mammograms every 2 years, what happens? Women tend to come every 5 years. During those 5 years, more cancers and more deaths.

Holly Holly
Wow. That’s shocking.

Harmony Harmony
Do governments know? By promoting 2 years, the result is returning for mammograms in 5 years?


By the way, this is a fact, and let me reference it. This is data from the Alberta Breast Cancer Screening Program, presented to the Alberta Society of Radiologists meeting in 2013 or 2014. Major screening programs and governments find this embarrassing, (and financially beneficial), so data like this doesn’t get publicity or published in journals.

Another example. Every few years, there will be some scientific study published somewhere, saying that mammography doesn’t prevent cancer deaths. A flurry of scientific rebuttals and arguing will appear in the medical journals for months afterwards. But normal people see none of that. Instead, normal people see a TV reporter telling women that mammograms don’t benefit, and they may see 2 doctors arguing about it on TV. The result? Women stop coming for mammograms for about 5 years, and during those 5 years, cancers happen and go undiagnosed too long, until they are big and involving lymph nodes, and more women die.

Megan Megan
Do the TV reporters know, that their little news report is going to kill people during the next 5 years?

Dr. Halls Dr. Halls
Nope. The only people who truly understand, are just a few senior epidemiologists who watch cancer rates rise and fall in waves, as years go by, and they can map the “mammography controversy TV stories” onto the waves.

Megan Megan
So, what about breast density?


Some of you may know that a patchwork of states in the USA have new laws requiring reporting of breast density. Here’s a map from 2014.


In a yellow-color state like Colorado, here’s the kind of message that goes in a letter to women:

“Your mammogram shows that your breast tissue is dense. Dense breast tissue is common and is not abnormal. However, dense breast tissue can make it harder to evaluate the results of your mammogram and may also be associated with an increased risk of breast cancer. This information about the results of your mammogram is given to you to raise your awareness and to inform your conversations with your doctor. Together, you can decide which screening options are right for you. A report of your results was sent to your physician.”

That letter will confuse women. It also confuses family doctors. I believe states that send confusing letters about mammography, will cause women in the state to have fewer mammograms, and therefore cause more cancer deaths in those states.

Dr. Halls Dr. Halls
Isn’t it crazy? The urge to do something that might prevent cancer deaths, can accidentally lead to more cancer deaths.

Megan Megan
So the forceful advocates who pushed these laws into existence, requiring breast density reporting, do they know this?

Dr. Halls Dr. Halls
No. They think they are helping. But I’m predicting that in 5 years there will be more cancer deaths in the yellow states, and in 10 years of arguing about it, the laws will still be there.

Holly Holly
I hope you’re wrong.

Tyler Tyler
Doc, you have no published evidence that the density laws and letters will be harmful. It’s just one mans opinion.

Talking Moose
Talking Moose
See how easy it is to discredit an opinion? All that matters is getting your mammogram.


My other website Breast-cancer.ca is where most of my breast cancer information has been accumulating.


  1. Vachon CM, van Gils CH, et al. Mammographic density, breast cancer risk and risk prediction. Breast Cancer Res. 2007 9:217.
  2. Assi V, Massat NJ, et al. A case-control study to assess the impact of mammographic density on breast cancer risk in women aged 40-49 at intermediate familial risk. Int J Cancer 2014:

Dr. Halls Dr. Halls
Even a webpage like this, with its discussion of controversy and confusion, might cause cancer deaths, if shared with negativity on facebook and argued about.

Talking Moose
Talking Moose
So if you like to argue in public…

Megan Megan
.. end with ‘just get your mammogram’.


Did you click on any faces or find other surprises?


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