Breast Density Not a Strong Risk Factor for Cancer

Posted on December 09, 2015

Marcia Frellick

Dense breasts are not a strong independent risk factor for breast cancer, according to a study of more than 52,000 mammograms.

On the basis of these findings, breast density should be considered one piece of the puzzle, along with factors such as age and family history, said Natasa Katavic, MD, from the Department of Radiology at Health Center Osijek in Croatia.

"We should examine all factors when we decide how often women should have examinations," she explained.

The results of the study were presented here at the Radiological Society of North America 2015 Annual Meeting.

Some previous studies have shown a link between breast density and breast cancer. And because cancers in dense breast tissue are harder to see on a mammogram, some women with dense breasts are advised to get additional screening with ultrasound or MRI.

The relevance of dense breasts has been widely debated in the United States, particularly because nearly half of all states have enacted legislation mandating the reporting of breast density to women who have undergone mammography, as previously reported by Medscape Medical News.

In their study, Dr Katavic and her colleagues looked at data from the National Breast Screening Program in Croatia for women 50 to 69 years of age, who are advised to get a mammogram every 2 years. They evaluated 52,962 mammography exams performed over 5 years at five different facilities.

Of the 230 breast cancers detected on mammography, according to criteria from the American Joint Committee on Cancer, 6% were stage 0, 47% were stage I, 17% were stage II, and 28% were stage III or IV.

Fatty vs Dense Breasts

When the patients were assessed according to American College of Radiology criteria for breast density, 47.6% of the breasts were classified as almost entirely fatty, 36.3% were classified as scattered fibroglandular densities, 13.2% were classified as heterogeneously dense, and 2.8% were classified as extremely dense.

Each woman with a detected cancer was age-matched with a control subject who lived in the same area.

The team expected to find more cancer in the higher-density breasts, but the opposite was true, Dr Katavic reported.

There was no significant difference in mammographic density between breast cancer patients and control subjects (Fisher's exact test, P = .083; odds ratio, 1.65; 95% confidence interval, 0.97 - 2.81; z = 1.85; P = .064).

This study suggests that density is not associated with a higher risk for breast cancer, which is important and warrants further research, said Laura Shepardson, MD, a radiologist at the Cleveland Clinic.

However, regardless of whether future studies show that density increases a woman's risk for breast cancer, "the sensitivity of mammography is still limited in women with dense breast tissue, since normal fibroglandular tissue can obscure an underlying small cancer," she told Medscape Medical News.

"We must continue to explore how best to screen for breast cancer through the use of either improved techniques, for example tomosynthesis, to reduce the masking effect of dense tissue or new tests that are not affected by breast density, such as blood tests," Dr Shepardson explained.