Breast density is linked to an increased risk of cancer, it also makes cancer harder to detect because dense tissue can hide tumors from X-rays.
However, new research indicates that not all women with dense breast tissue are at very high risk.
Dense breasts have a relatively high proportion of glandular or connective tissue which shows up as white on mammograms. Tumors also appear white, so sometimes dense tissue can hide them. Non-dense breasts have more fat, which looks ark on mammograms, so tumors stand out more easily.
Patient advocates urge women with dense breasts to speak with their doctors about extra tests like ultrasound or an M.R.I. to check for tumors that mammography may have missed. Studies have found that these additional exams can improve detection of tumors over mammography alone in dense breasts.
22 states have passed laws which require breast density to be reported by mammography patients. Similarly, federal legislation has recently been introduced in the House and the Senate.
This new study was published on Monday in the Annals of Internal Medicine.
The study suggests that only about half of women with dense tissue are at such a high risk that they need extra tests. Doctors should not look at density alone but should consider other risk factors when making decisions about additional screening.
The study findings are based on the medical records of 365,426 women ages 40 to 74 who had screening mammograms from 202 through 2011. The goal to find out if it was possible to detect whether, among all the women with dense breasts, any distinct subgroups had a higher risk than others of developing cancer.
The study found that women with certain combinations breast density and five year risk levels had the highest odds of cancer. Two groups had high rates of interval cancer, defined as more than one case per 1,000 mammograms.
Although mammography is currently the best screening tool at the moment unfortunately, for certain women mammography is not enough.
The study was conducted in part because a number of doctors thought that the laws and advocacy groups had gotten ahead of the science. About 45% of all women have dense breasts, but not all women with dense breast have a high risk of cancer. Some experts warn that the new laws would give some women bad news which does not necessarily apply to them and lead them to ask for unnecessary, expensive tests that could swamp the health care system.
