Q: My mammogram report noted I had dense breasts. What does this mean?
A: Breast cancer is the most common cancer diagnosed in women, affecting up to one in eight women in their lifetimes; almost 250,000 women were diagnosed with it in 2013. Since the introduction of mammography screening, mortality from breast cancer has decreased by 30 percent; however it is still the second-most common cause of cancer death in women and almost 40,000 died from it in 2013.
Breasts are made up of fibrous connective tissue and fatty tissue that give them their shape and size, glandular tissue, which produces the milk in lactating women and ducts that carry the milk. Breast density refers to the amount of glandular and fibrous tissue (which absorb X-rays and hence appear white on radiographic images, so are called “X-ray-dense” tissues) as opposed to fatty tissue (which appears dark on radiographic images); breast density is not related to the firmness of a woman’s breasts, it is a factor of how much X-ray energy is absorbed.
Breast density is determined by the appearance of the breast tissue on a mammogram and is categorized on a bi-rads (Breast Imaging Reporting and Data System) scale of 1-4; bi-rads 1 breasts have less than 25 percent dense tissue, bi-rads 2 have between 26 and 50 percent, bi-rads 3 have 51 to 75 percent and bi-rads 4 have more than 75 percent dense tissue.
Younger women usually have dense breasts, however as women age their breast density often decreases. Despite this, about 40 percent of American women over age 50 still have dense breasts (bi-rads 3 or 4); this is even more common in Chinese women, with over 70 percent having dense breasts after age 50.
Breast density is important because of the medical ramifications it has:
Mammography is able to detect almost all cancers that exist in women with fatty breasts; one study noted up to 98 percent could be identified. This is because cancer tissue is typically radiographically dense, appearing white on a mammogram and easily seen in contrast to the black-appearing fatty breast tissue images. However, X-ray absorption by the dense fibrous or glandular tissue make the mammogram image appear white, masking the ability to identify cancer; studies have shown that mammography is only 60 percent or less sensitive in women with dense breasts.
Women with dense breasts have a significantly increased risk of developing breast cancer, as much as four to six times higher than women with fatty breasts. Because women with dense breasts are at an increased risk of developing breast cancer but mammography is not as sensitive in detecting it, other imaging modalities to supplement mammography screening, such as ultrasound or MRI, may be considered.
MRI as a supplement to mammography is very sensitive for identifying cancer, but it may give “false positives” where it indicates the possibility that there is cancer where none actually exists. For women at very high risk of developing breast cancer (such as women with a strong family history of it or those with a genetic predisposition like Angelina Joile has), screening MRI is recommended by the major cancer societies; however there are presently no specific guideline recommendations for the use of MRI as a supplement to mammography for screening of women with dense breasts.
Page 2 of 2 - Ultrasound as a supplement to mammography is very good at identifying cancers that may be missed by mammography alone. Ultrasound is a common imaging modality used to follow up equivocal or suspicious findings from a screening mammogram, and an automated breast ultrasound device was recently approved for breast cancer screening as a supplement to mammography for women with dense breasts. However, there are no specific guideline recommendations from any of the major cancer societies for using ultrasound as a supplement to mammography for screening women with dense breasts.
Despite the lack of specific guidelines (research and evaluation for developing these is ongoing), many state legislatures (12 as of August 2013, with other states just about to enact similar requirements) have passed laws requiring women to be notified of their breast density status, and four states also require insurance to cover supplemental screening. The FDA is considering a regulatory amendment to make breast density notification a national standard for all mammogram reporting, and Congresswoman Rosa DeLauro of Connecticut and many of her colleagues in Congress have introduced breast density reporting legislation.
We need to do more to combat breast cancer. Personalizing screening for women with dense breasts by augmenting mammography with another screening modality shows promise to save even more lives.
Jeff Hersh, Ph.D., M.D., can be reached at DrHersh@juno.com.