Oct. 7, 2010 -- Women with an early form of breast cancer are at higher risk for recurrence if their breast tissue appears dense on mammograms, a study shows.
The study also shows the risk of recurrence is more pronounced in the opposing breast.
The new findings appear in the Oct. 7 issue of Cancer Epidemiology, Biomarkers & Prevention.
In the study, of 935 women with an early type of breast cancer known as ductal carcinoma in situ (DCIS) treated with breast-conserving surgery, those women whose breasts appeared dense on their screening mammogram were twice as likely to develop a secondary breast cancer. This risk was about threefold higher for developing a secondary breast cancer in the opposite breast, the study shows.
DCIS refers to breast cancer that has not spread outside the milk glands. During follow-up, 164 had a subsequent breast cancer on the same breast and 59 developed a new cancer in the other breast.
"Breast density is among the strongest risk factors for breast cancer, like family history," says study researcher Laurel A. Habel, PhD, research scientist at Kaiser Permanente's Division of Research in Oakland, Calif.
Composed of breast ducts and connective tissue, dense breast tissue looks white on mammograms. Non-dense breast tissue is mainly fat and appears dark gray on a mammogram.
Exactly how dense breast tissue increases breast cancer risk is not fully understood, but breast density may be mediated by certain hormonal and genetic factors. That said, certain hormone therapies can increase or decrease breast density and should be discussed with a doctor if a woman has dense breasts.
"There is very little public awareness that background density of breast tissue on a mammogram is a risk factor for breast cancer," says Philadelphia-based oncologist Marisa Weiss, MD, the president and founder of the advocacy group Breastcancer.org and the author of several books, including Taking Care of Your Girls: A Breast Health Guide for Girls, Teens, and In-Betweens.
"Breast density defined by mammography is something to be aware of," she says.
When reading mammography results, many women -- and doctors -- look for the words normal or abnormal (meaning possible cancer), and don't pay attention to density, she says.
Weiss was diagnosed with breast cancer in April 2010. She had a family history of breast cancer and dense breasts on mammogram, so this study resonates with her on a personal level.
According to the National Cancer Institute, women who have a high percentage of dense breast tissue have a higher risk of breast cancer compared to those of a similar age who have a small percentage of or no dense breast tissue.