What You Really Need To Know About Dense Breasts

By Michael Misialek, M.D.
Guest Contributor

Reading the pathology request on my next patient, I saw she was a 55-year-old with an abnormality on her mammogram. Upon further investigation I discovered she had dense breasts and a concerning "radiographic opacity." The suspicion of cancer was high based on these findings and so, a breast biopsy had been recommended. As I placed the slide on my microscope and brought the tissues into focus, I immediately recognized the patterns of an invasive cancer. Unfortunately the suspicion had proven correct.

Just a few patients earlier, an almost identical history had prompted another breast biopsy. This time the results were far different, a benign finding and obviously a sense of relief for the woman. Every day these stories unfold; the never ending workup of abnormal mammogram findings. Both radiographically and microscopically, it can be challenging at times sorting out these diagnoses, particularly in the face of dense breasts.

But what, exactly, are dense breasts and why are they suddenly in the news?

Breast Tissue 101

Breast tissue is actually made up of three tissue types when viewed under the microscope. The percentage of each varies between patients. There is fat, fibrous tissue (the supporting framework) and glandular tissue (the functional component). This is what I actually see under the microscope. Cancer can occur in fatty or dense breasts. It can be toughest to assess when the background is dense.

Biopsy, considered the gold standard in diagnosis, may even prove difficult to interpret when in the background of dense breasts. Dense breasts can hide a cancer, making it more difficult to detect both by mammogram and under the microscope.

Breast density has taken a lot of heat recently. A new study published in the Annals of Internal Medicine found that not all women with dense breasts and a normal mammogram warranted additional screening, as was previously thought. Understandably this report has received much attention. The authors found nearly half of all women had dense breasts. This alone should not be the sole criterion by which additional imaging tests are ordered since these women do not all go on to have a cancer. Clearly other risk factors are at play.

Confusion All Around

This is confusing for patients and doctors alike, especially when it seems as if screening guidelines are a moving target. Recently, the American College of Physicians issued new cancer screening guidelines: among these was mammograms, being recommended every two years. This too is getting a lot of press.

The American College of Radiology, American Cancer Society, Society of Breast Imaging and American College of Obstetricians and Gynecologists recommend yearly mammograms beginning at age 40.

Breast density is a subjective factor measured by the radiologist and is reported using the Breast Imaging Reporting and Data System. This ranges from almost entirely fatty to extremely dense. The Massachusetts Radiology Society provides an overview of the BI-RADS categories which are based on four measures of increasing density.

Currently 21 states now require providers to inform patients whether they have dense breasts — Massachusetts is one of them. The law is far from perfect. There is variability in how results are provided.

And there are other problems: increased false positive rates from using additional tests such as MRI and ultrasound, not to mention the increase costs associated with such screening. Most states do not mandate insurance coverage in these circumstances. Currently it has proven cost effective in only high risk patients. It is unknown how and if additional screening methods should be employed in those with average risk. Despite these problems, mammogram is still the best screening method, having been documented to reduce breast cancer deaths.

But imaging alone should not be assessed in a vacuum. Individual risk stratification is needed, emphasized by the Annals of Internal Medicine study. The Massachusetts Radiology Society offers resources for both patients and doctors.

There are also calculators available to help assess a woman’s risk of developing breast cancer. These typically factor in age, race, family history, a history of breast biopsy and density.

Biopsy interpretation by pathologists has come under controversy recently where a study in the Journal of the American Medical Association found diagnostic discordance among pathologists when presented with grey zone diagnoses.

What do we know about the pathology and population trends of those undergoing screening mammograms is that we are definitely diagnosing breast cancer more frequently. Breast density does play a factor. Those with dense breasts or a positive family history have a higher likelihood of being diagnosed with cancer.

However breast density is not the only factor. As the Annals study found, a patient’s personal, genetic and family history are all important in gauging individual cancer risk. This underscores the importance of collaborative care and shared decision making between a patient and their doctor. The extended care team, including pathology, radiology, surgery, oncology and primary care, collectively work to deliver personalized care.

An educated patient is our greatest asset. Be your own advocate. Ask questions and learn. As I finalize the report on my patient, I page radiology to discuss the findings. The dominoes have been set in motion.

Dr. Michael Misialek is associate chair of pathology at Newton-Wellesley Hospital and assistant clinical professor of pathology at Tufts University School of Medicine.


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