Reading your Mammogram Report: Why Density Matters

It’s not enough to read: “Your recent mammogram appears normal. Recommend annual screening mammography in one year.” In fact, 28 states have now passed laws that require mammogram reports also include notifications to patients and physicians regarding the individual’s breast tissue density. Why? The breast tissue density measures:

(1) How good is your mammogram for detecting a possible cancer; and,

(2) What potential risk for breast cancer do you have as an individual?

Mammogram pictures are black, white, and varying shades of gray, corresponding to breast tissue composed of fat (seen as dark) and fibroglandular tissue (seen as white), which is fibrous connective tissue and hormonally-stimulated gland tissue. The greater the amount of white fibroglandular tissue in the breast, the more “dense” the category on the mammogram, and the greater the likelihood that a cancer, which also is white, may hide in the dense, normal white tissue. Not surprisingly, the dense glandular tissue, which has higher cellular activity, turnover, and potential for mutation, also has the highest risk for developing a breast cancer. Research now shows that the higher the density, the greater the patient’s risk for developing malignancy, and those tumors detected in dense breasts are of increased size and worsened prognoses.

Your report should therefore describe your breast tissue in one of four categories, according to the Breast Imaging Reporting and Data Systems (BI-RADS):

  1. Almost entirely fatty
    • Approximately 14% of the population age 40-74
    • Less than 25% of the breast tissue is white fibroglandular tissue
    • No increase in risk for breast cancer
  2. Primarily fatty with scattered fibroglandular densities
    • Approximately 38% of the population age 40-74
    • Between 25-50% of breast tissue is white fibroglandular tissue
    • No significant increase in risk for breast cancer
  3. Heterogeneously dense, which may obscure small masses.
    • Approximately 34% of the population age 40-74
    • Between 51-75% of breast tissue is white fibroglandular tissue
    • “Heterogeneous” means many different types, seen as a patchy white appearance on the mammogram that may mask lesions, benign or malignant
    • 2-fold increased risk for breast cancer
    • Benefit from addition of 3D-tomosynthesis
  4. Extremely dense breast tissue, which lowers the sensitivity of mammography.
    • Approximately 7% of the population age 40-74
    • Greater than 75% of breast tissue is white fibroglandular tissue
    • 5-fold increased risk for breast cancer (equivalent risk to having 2 relatives with breast cancer)
    • Benefit from addition of screening whole breast ultrasound

Both of the ‘Heterogeneously’ dense and ‘Extremely’ dense categories together represent 43% of our 40-74 year-old population, of whom 45% are between 40-50 years old – breast tissue density decreases with increasing age and decreasing hormones. These dense tissue findings warrant notification to the patient that mammography is somewhat limited, or limited. And this must be stated in lay language that is understandable to patients with poor literacy, disparities, and limited access to care. Besides state laws, a Breast Density Reporting amendment to the Mammography Quality Standards Act (MQSA) is in a “Notice of Proposed Rulemaking” this year.

Identification of a patient with heterogeneously dense or extremely dense breasts raises consideration for additional screening tools with 3D tomosynthesis and/or supplemental whole breast ultrasound, if available. Women with heterogeneously dense breasts are demonstrated to have increased cancer detection and reduced recall rates with addition of 3D-tomosynthesis . 3D-tomosynthesis is not shown to be of benefit in the small population of women with extremely dense breast tissue (possibly due to small number in study ), who benefit more from the addition of ultrasound screening. An MRI would not be indicated for increased breast tissue density alone, which is considered to confer a moderate lifetime risk (15-20%; MRI screening is warranted for women with >20-25% lifetime risk calculations). Unfortunately, these additional screening tests may not be covered by insurance (Affordable Care Act covers screening mammography; some states, such as New Hampshire, require insurance to cover screening 3D-tomosynthesis). Furthermore, these additional screening tests often find 10-20 more “false-positives” for every additional cancer detected, so individual risks, benefits, and personal risk aversion must be discussed with one’s physician before pursuing more ancillary screening. The impact of breast density legislation in California, as studied by Dr. Lina Nayak at UCSF, has resulted in supplemental screening with handheld whole breast ultrasound (WBUS) and tomosynthesis being offered at more than 33% of facilities.

In conclusion, breast density must be considered in assessing an individual’s risk for breast cancer as well as the potential for a masked malignancy hiding in dense tissue. Patients with dense breasts should know they face an elevated breast cancer risk, regardless of family history, which may be reduced by exercise, good diet, Vitamin D, limited alcohol, and, in select cases of further increased risk, treatment with Tamoxifen, Arimidex, or other aromatase inhibitors. Women also should know the limitations of their mammograms in the setting of dense breasts, their options for ancillary screening, and their own “normal” self-breast physical exam such that changes may be reported to their physicians. Finally, women with dense breasts, in particular, should consider owning their own “medical picture album” for electronic access and control of all images (all information) essential to their health. Visit, a part of lifeIMAGE, to learn more about secure, online storage and sharing of mammograms.  Click here for complete list of resources used for this article.


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Kathryn Pearson Peyton

by Kathryn Pearson Peyton
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