Breast density refers to the ratio of fatty tissue to glandular tissue (milk ducts, milk glands and supportive tissue) on a mammogram. About 50% of women have increased density ("dense breasts") as they have an increased amount of glandular tissue compared to fatty tissue. Younger women, premenopausal women and women using hormone replacement therapy are more likely to have dense breasts. Dense breasts place women at increased risk of breast cancer and later diagnosis, in part, because breast cancers are more difficult to see on mammography in women with increased breast density.
In 2003, Nancy Cappello, Ph.D., was diagnosed with a stage III breast cancer only a short time after having a normal mammogram. She had dense breasts but did not know that it put her at higher risk for a cancer or that it could make a cancer more difficult to detect. She lobbied in her home state of Connecticut for insurance coverage for ultrasounds for dense breasts which was enacted in 2005. She then worked towards a law requiring women to be notified of their breast density. In 2009, Connecticut became the first state with mandatory density notification. Federal breast density notification laws have been introduced but none yet passed.
As of January 2017, there are 31 states with laws requiring women to be notified of their breast density on their mammograms. Four additional states have laws recommending but not requiring notification. Only 4 states have laws requiring insurance coverage for additional imaging for women with dense breasts. For a map indicating states with density notification laws, go to densebreast-info.org/legislation.aspx.
There are currently no national guidelines for additional screening of dense breasts.