MAKING SENSE OF BEING DENSE

Diagnostic Radiologist with Milwaukee Radiologist, LTD and currently with Covenant Medical Center

“Detection of breast cancer is difficult by mammogram in dense breasts . . .” As women are well aware, the purpose of a mammogram is to screen for breast cancer. What many women may not know is that radiologists assess the level of density (proportion of breast and connective tissue compared to fat) in each mammogram to determine sensitivity to detect cancer. Approximately 40 - 50 percent of U.S. women, who have mammograms, have dense breasts. It is important for women and referring physicians to understand that dense tissue is defined by mammography, not by palpation. Many women mistakenly believe they have ‘dense’ tissue due to the fact they have lumpy breasts when, in fact, they are quite fatty. Breast cancer is typically white on mammogram. Since fatty breasts have a dark background appearance, it is relatively easier to spot the white cancers. However, breasts that have more connective and glandular tissue are denser, and appear whiter on mammograms, which makes detection of small early breast cancers difficult to extremely difficult. Some experts liken it to trying to find a snowball in a snowstorm. The sensitivity for detection of breast cancer varies between 30% for extremely dense breasts to 80% for fatty breasts. Not only is detection of breast cancer difficult by mammogram in dense breasts, but having dense breasts is considered one of several other risk factors for breast cancer. Some authors have suggested 4 to 6 times increased risk of developing breast cancer in women with dense breasts compared to women with fatty breasts. Hence, given the relatively diminished performance of mammography in women with dense breasts and the increased risk for breast cancer, there has been a recent wave to evaluate supplemental screening by other modalities for women with dense breasts. FDA mandates that dense breast tissue notification be included in the formal mammography report sent to referring physicians, which has practiced throughout the nation for more than a decade. Recently, in seven states—Connecticut, New York, Texas, Virginia, Maryland, Hawaii and California —the plain-language report that women receive following their regular screening mammograms must now include information regarding whether they have dense breast tissue. With mammography density notification legislation pending in at least 18 more US states, including Iowa, and a bill introduced in the US House of Representatives, a large number of women in due time, across the country may be learning more about their mammographic breast density in their plain-language letters. This information is provided to raise awareness and to encourage women to start discussions with their doctors to determine whether additional screening options may be right for her. Most breast imagers believe that every woman has a right to know her mammographic breast density, but what is unclear is what the patient could do with that information. There are still many unanswered questions about the biology of breast cancers and breast density. Assessing breast density on a mammogram is sometimes subjective and can vary between radiologists. Many women, when told they have dense breast tissue, may feel that they absolutely must have additional testing. Others may be anxious or confused and drop out of screening altogether. However, it is important to have as much information as possible and realistically discuss risk/benefits. Screening Modalities - In the realm of screening mammography, it is clear that digital mammography has improved performance than film screen mammography in dense breast women and that Tomosynthesis (3D mammography) has superior performance than 2D digital mammography in all types of breast composition. The additional screening modalities that are available to patients are whole breast ultrasound and breast MRI. While there is improved sensitivity when screening ultrasound or MRI or both are included along with mammography, it is also known that ultrasound and MRI tend to find more false-positives, thereby increasing unnecessary biopsies and creating additional healthcare costs. Since mammography is the only modality where mortality benefit has been documented, ultrasound or MRI screening are only to be considered as supplemental to mammography and not as a substitute to mammography. High Risk Women - American Cancer Society, American College of Radiology and National Comprehensive Cancer Network categorize women as high risk if they have any of the following risk factors. • BRCA mutation • First-degree relative of BRCA carrier, but untested • Lifetime risk 20–25% or greater, as defined by risk assessment models that are largely dependent on family history like Tyrer-Cuzick, BRCAPRO, BOADICEA • Radiation to chest between age 10 and 30 years • Li-Fraumeni syndrome, Cowden and Bannayan-Riley-Ruvalcaba syndromes and their first-degree relatives Since the combined sensitivity of mammography and sonography is only 52%, compared to 92.7% for combined mammography and MRI, in high risk women, breast MRI is recommended over sonography as supplemental screening modality in this population. Since 2007, insurance companies have been covering annual screening breast MRI in the above mentioned high risk women. Most of these women are typically younger and tend to have dense breasts on mammogram. Currently, there is insufficient evidence to recommend for or against MRI screening in women with intermediate lifetime risk, which includes women with 15–20% lifetime risk, those with only heterogeneously or extremely dense breast on mammography or only with a personal history of breast cancer. In these patients, American Cancer Society recommends that insurance payment should not be a barrier and that screening decisions should be made on a case-by-case basis, as there may be particular factors to support MRI. In several US states, screening ultrasound is being utilized as an adjunct to mammography to screen women with dense breasts who may not qualify for breast MRI. Advantages to the incorporation of sonography into a breast cancer screening program include the fact that breast ultrasound is well tolerated, noninvasive, and relatively inexpensive. Also, it is easy to biopsy lesions seen only by sonography. However, limitations are also evident. The examination is operator dependent, and the skills of individual technologists and radiologists are variable. While cancers detected with screening sonography have generally been stage I invasive breast cancers, there is no data to assess the ability of sonographic screening to decrease breast cancer mortality. Another issue is reimbursement of screening breast ultrasound by insurance is questionable and many patients may have to pay out of pocket for this test, possibly a few hundred