Women with dense breasts not only have a more difficult time having breast cancer detected but also have a three times greater risk of cancer, according to a study published in the New England Journal of Medicine. Breast density is measured according to a ratio of lean to fatty tissue. About one in six women have denser tissue.

A study recently conducted by Canadian researchers looked at more than 2,000 women who were screened for breast cancer and found that:

• Women with dense breast tissue in 75 percent or more of the mammogram had nearly a fivefold increased risk of breast cancer compared with women with dense breast tissue in 10 percent of the mammogram;
• For younger women (those younger than 56 years of age), 26 percent of all breast cancers and 50 percent of breast cancers detected less than one year after a negative mammogram were associated with dense breast tissue in 50 percent or more of the mammogram; and
• Dense breast tissue most likely masks breast cancers that would otherwise be found by mammography screening.

An editorial accompanying the NEJM article said that most women don’t know if they have dense breasts so their doctors should discuss it with them and recommend screening methods other than mammography. The American Cancer Society, which recommends annual mammograms for women over 40 years old, says it will consider whether women with dense breasts should receive additional screening with an ultrasound after results from another study are released later this year.