Breast Density and Optimal Breast Health Assessments

If you had a mammogram recently, you may have noticed a new policy concerning women with dense breasts.  This policy is based on recent legislation, known as “Dense Breast Bill HB467”, which was passed by the General Assembly of North Carolina in October 2013.  The NC Department of Health and Human Services Division of Health Service Regulation subsequently issued a bulletin to all radiologists clarifying what must be contained in correspondence sent to patients identified as having very dense breast tissue.

As of January 1, 2014, all healthcare facilities equipped with radiology services that provide mammograms have been required to include the following statement in the summary of each mammography letter if the patient has been identified as having very dense breast tissue:

“Your mammogram indicates that you may have dense breast tissue. Dense breast tissue is relatively common and is found in more than forty percent (40%) of women. The presence of dense breast tissue may make it more difficult to detect abnormalities in the breast and may be associated with an increased risk of breast cancer. We are providing this information to raise your awareness of this important factor and to encourage you to talk with your physician about this and other breast cancer risk factors. Together, you can decide which screening options are right for you. A report of your results was sent to your physician.”

The challenge of dense breast tissue is basically threefold.  First, as noted above, it is difficult to detect a possible tumor in women who have dense breast tissue.  Second, very dense breast tissue on a mammogram (mammographic density) is considered to be among the strongest risk factors for breast cancer.   And third, women with denser breast tissue also tend to have more recurrences and more aggressive disease than women with less dense breast tissue.

What this means is that mammography may miss some types of breast cancer that are likely to be more dangerous once diagnosed.  This was one of the arguments used by the U.S. Preventive Services Task Force  when it recommended in 2009 against mammograms in women under age 50.  A high percentage of these younger women have very dense breasts. 

Why does breast density reduce the diagnostic sensitivity of a mammogram?  The problem is due to a masking effect: both dense breast tissue and cancer appear white on mammogram, making it difficult to distinguish between the two tissue types.  We now know that women diagnosed with an interval breast cancer—that is, a cancer found after the mammogram was negative—may be six to nine times more likely to have highly dense breast tissue than fatty breast tissue.

Breast thermography, or breast thermal imaging, is a method that measures temperature changes on the surface of the skin, indicating physiologic changes (inflammation, angiogenesis, etc.) that could help predict a greater likelihood of developing breast cancer. 

The sensitivity of breast thermal imaging is not affected by breast density.  A series of abnormal thermograms can be used to determine whether a woman may be in a “high risk” situation for developing breast cancer, and thus can help with the design of a program for changing the conditions that would support the cancer’s growth and progression.

A well-designed clinical study out of the Cambridge Breast Unit of Addenbrooke's Hospital in Cambridge (UK) sought to evaluate the combination of breast thermography with mammography for women under age 50.   Again, it is well established that younger women tend to have denser breasts than older women.  The Cambridge study showed found an 89% sensitivity for the combined approach, which is substantially higher than the typical sensitivity (range of 30-60%) of mammographic screening for women with dense breasts. 

A second study at the New York Presbyterian Hospital-Cornell in New York City found that breast thermography resulted in 97% sensitivity in women with dense breasts.  This study was not blinded, however, and thus is considered less rigorous than the Cambridge study.

Though we do not advocate replacement of mammography with breast thermography, we do suggest using the latter modality to obtain more comprehensive information about the conditions in the breast that could eventually lead to breast cancer.  Much research now suggests that the addition of breast thermal imaging greatly improves the sensitivity of mammography, i.e., it’s ability to detect a possible tumor.  In high-risk young women with dense breasts, a persistently abnormal thermogram could warrant the use of an MRI to compensate for the possibility of a false-negative mammogram.


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