About four out of 10 women have dense breasts. Density has nothing to do with size—it just means that dense breasts have more connective tissue than fatty tissue. Women with dense breasts are five times more likely to develop breast cancer than other women.

Denser breasts also make breast cancer harder to find because both cancers and dense connective tissue areas look the same on a mammogram. They both appear as thick white globs. Fatty tissue appears dark and transparent, so tumors show up more easily. In fact, dense breasts reduce the ability of mammograms to find cancer by about 50 percent.

Higher Risk and Hard to Find

To learn more about why dense breasts develop more cancers and how to find these cancers on an imaging study, researchers from the Linköping University in Sweden used two technologies. One is an MRI imaging study with a contrast dye that can measure the movement (diffusion) of water molecules through breast tissue. The other is called microdialysis: This technology measures the fluid between breast cells, called the microenvironment.

The results of the study are published in the British Journal of Cancer. Forty-four women with healthy breasts had their breast density measured by a mammography exam called the Breast Imaging Reporting and Data System (BI-RADS). Breast density in the study group ranged from non-dense to dense. All the women were postmenopausal.

Microdialysis was done by placing a small tube (catheter) into breast tissue to withdraw a fluid sample. The study found that women with dense breasts had higher levels of 124 proteins. These proteins are linked to faster cell growth, more blood vessel growth and inflammation. All of these factors are associated with cancerous tumor growth. The imaging studies found that breast perfusion (or passage of blood volume) was delayed in dense breasts.

A New Kind of MRI

An MRI picks up more growths (or lesions) in dense breasts than a mammogram, but it cannot determine the difference between a cancerous and noncancerous lesion. The researchers propose that the new imaging technique of an MRI along with perfusion measurement could be a way to identify tumors in dense breasts. This combo type of imaging may also reduce unnecessary biopsies.

A Way to Lower Cancer Risk?

The study also suggests that altering the microenvironment in dense breasts could reduce cancer risk. This could be done by reducing or blocking these proteins. About one-third of women between the ages of 40 and 50 have cells in their breasts that have the potential to become cancerous, but only about one percent of these women develop cancer. This study suggests that density of breast tissue and the microenvironment may be a key to identifying women at risk. Altering the microenvironment may offer new ways to prevent or reduce the risk of breast cancer in dense breasts. The next study for the research team is to find out if anti-inflammatory treatment can change the cancer risk in dense breasts.

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