What does it mean when you are told you breasts are dense?
Breasts are made up of a mixture of fat and breast tissue. The denser the breast, the more breast tissue you have. Mammograms work by “looking through” the fat to see the breast tissue. If you have dense breast tissue, particularly in a large breast, it means there are parts of the breast which are not visible. This is why when they do a mammogram they smash your breast as flat as they can. They want to see as much of the breast tissue as they can.
Your breast composition changes as you age and with pregnancies. Usually in older women, the breast becomes fattier.
Having dense breast tissue may increase your risk slightly of getting breast cancer. (This is likely the same reason breast reductions reduce your risk of breast cancer–the more breast tissue you have, the higher the risk a cell can go wayward and change into cancer.) Mammograms may be less accurate in women with dense breasts, as masses which are benign (okay) and malignant (not okay) both appear white.
What is the rate of breast density?
- 10% of women have almost entirely fatty breasts
- 10% of women have extremely dense breasts
- 80% are in one of 2 middle categories.
Radiologists classify breast density using a 4 level density scale:
- A – almost entirely fatty
- B – scattered areas of fibroglandular density
- C – Heterogeneously dense
- D – Extremely dense
What should you do if your breasts are dense?
If you have extremely dense breasts, you may want additional screening exams, as mammograms may not be able to see through the entire breast. The most common other tests are MRI and ultrasound. Of note, these tests may find things which are not cancer, but when found may require added testing and unnecessary biopsies. Also the cost of the ultrasound and MRI may not be covered by insurance. In California since 2013, they have a Breast Density Law.
Points of this law:
- Starting April 1, 2013, California law requires patients be told if they have dense breast tissue mammogram, and if so, they can discuss screening options.
- Approximately 50% of women have “heterogeneously dense” or “extremely dense” breasts. For all of these women, the patient letter informs them they have dense breast tissue.
- Only 10% of all women have extremely dense breast tissue This is associated with a relative 2 times increased risk of breast cancer than women with average breast density.
- 40% of women have “heterogeneously dense” breast tissue. The increased risk for them is 1.2, so breast density is not a major cancer risk factor.