Study: Breast Density May Not Call for More Screening
As the debate continues to swirl around the medical significance of dense breasts and whether extra screening should be done, a new study led by University of California, San Francisco (UCSF) researchers has found that women with dense breasts may need only routine mammograms unless they are already at high risk for breast cancer.
In their paper, the researchers said that five-year breast cancer risk is a critical component in deciding whether supplemental screening is justified. Breast density should not be the sole factor in this decision because not all women with dense breasts are at high risk for cancer. The study was published May 19 in Annals of Internal Medicine.
The research focused on approximately 365,000 women between age 40 and 74 who had undergone a regular digital screening mammogram and had no history of breast implants or breast cancer.
Breast density is determined only by mammograms; breasts are considered dense if the woman has a lot of fibrous or glandular tissue but not much fatty tissue, according to the American Cancer Society. The reason for the concern over mammogram frequency is that having dense breasts makes it more difficult for X-rays to pass through the breast tissue and can mask tumors.
"Not all women with dense breasts have a high enough risk of cancer to justify supplemental screening," says lead author Karla Kerlikowske, MD, a professor of medicine, epidemiology, and biostatistics at UCSF and a primary care physician at the UCSF-affiliated San Francisco VA Medical Center. "We found that for the vast majority of women undergoing mammography—including those with dense breasts but low five-year breast cancer risk—the chance of developing breast cancer within 12 months of a normal mammogram was low. Women with extremely dense breasts and intermediate to high five-year breast cancer or heterogeneously dense breasts and high five-year breast cancer risk were at highest risk for developing breast cancer after a normal mammogram.
"Our findings can help guide women and providers in discussing supplemental imaging and whether to consider extra testing," Kerlikowske adds. "This study provides a starting point to identify women who may have the most to gain from supplemental imaging or alternative imaging strategies."
Currently, 24 states require that women be notified if they have dense breasts. The laws also encourage women to discuss supplemental screening with their medical providers. Similar legislation, which would set a minimum standard for notification and recommend that women discuss with their doctors whether further screening is necessary, is pending in Congress. This would have a considerable impact nationally, affecting tens of millions of women annually.
Digital mammography, used by the vast majority of mammography facilities, detects 81% to 87% of breast cancers among women 40 to 79 years old, according to the authors. But its ability to detect breast cancer in women with extremely dense breasts is lower.
As a result, supplemental imaging has been suggested for women with dense breasts to heighten their chances for tumor detection before they become symptomatic. While supplemental imaging for women with dense breasts can increase cancer detection, it can also lead to more false-positive results and more unnecessary biopsies.
In the prospective cohort study, the researchers drew upon statistics from 2002 to 2011 and analyzed screening data collected by the Breast Cancer Surveillance Consortium (BCSC). Overall, nearly one-half of the women in the study had dense breasts, and the proportion with heightened five-year risk was highest among those with extremely dense breasts.
"We found that, rather than using only breast density to decide whether women with dense breasts should be considered for supplemental imaging, breast cancer risk should also be taken into consideration," says Kerlikowske, a member of the breast oncology program at the UCSF Helen Diller Family Comprehensive Cancer Center. "The BCSC risk calculator that includes age, family history of breast cancer, history of breast biopsy, breast density, and race can be used to calculate five-year breast cancer risk. Determining breast cancer risk along with knowing a woman's breast density will optimize the identification of women with high interval cancer rates who may benefit from supplemental screening."
The authors noted that they were unable to assess the benefits of patient discussions with providers about supplemental breast imaging.
— SOURCE: University of California, San Francisco