Screening mammography may now be safely extended to once every 3 years for women 50 years of age and older provided they do not have dense breasts and are at low risk for breast cancer, new joint recommendations from the United States indicate.
Conversely, women who have known risk factors for breast cancer and whose breasts are dense should probably be screened yearly, the same recommendations suggest.
"The United States Preventive Services Task Force (USPSTF) recommends biennial screening for average-risk women but with this approach, the benefits are modest and the harms significant," lead author Amy Trentham-Dietz, PhD, University of Wisconsin-Madison Carbone Cancer Center, told Medscape Medical News.
"So we believe that by examining screening intervals based on risk and breast density, we could improve the benefit-to-harm balance for women and while we still agree that women between 50 and 74 years of age should obtain mammograms, the frequency should depend on more than just a woman's age."
The study and an accompanying editorial were published onlineAugust 22, 2016 in the Annals of Internal Medicine.
Various Screening Intervals
The Cancer Intervention and Surveillance Modeling Network collaborated with the Breast Cancer Surveillance Consortium (BCSC) to evaluate various screening intervals for digital mammography among women based on age, risk for breast cancer, and breast density. Women with known genetic risk factors, including mutations in breast cancer susceptibility genes, were not included in the analysis.
Three different models were used to predict the benefits and harms of screening mammography for women aged 50 to 74 years who were deciding to initiate or continue biennial screening until 74 years of age.
Outcomes were then compared with matched outcomes that would have occurred if the same women had undergone annual or triennial screening mammography.
Investigators stratified women into four relative risk categories based on common risk factors, such as postmenopausal obesity, a history of benign breast biopsy results, and a history of lobular carcinoma in situ.
"For all screening intervals, as risk and breast density increased, the benefits (breast cancer deaths averted, life-years gained, and QALYs [quality-adjusted life-years] gained) of screening increased and the harms (false-positive mammograms, benign biopsy results, and overdiagnosis) decreased with greater risk," Dr Trentham-Dietz and colleagues report.
For example, among average-risk women with fatty breasts, screening every other year averted a median of 4.1 and 5.3 deaths from breast cancer per 1000 women screened compared with no screening.
Benefits of biennial screening were similar in average-risk women with scattered fibroglandular density, where a median of 5.2 to 6.5 deaths from breast cancer would be avoided compared with no screening.
"Screening outcomes were similar for triennial screening compared with no screening in average-risk women with low breast density," Dr Trentham-Dietz and coauthors continue. Here, the number of breast cancer deaths averted would range from 3.4 to 5.1 for every 1000 women who underwent screening compared with no screening, they note.
Furthermore, there would be between 21% and 23% fewer false-positive mammograms if average-risk women with low breast density underwent triennial screening vs biennial screening; and there would also be 13% to 17% fewer benign biopsies and between 8% and 20% fewer cases of overdiagnosis with the triennial approach.
Among intermediate-risk women with fatty breasts, screening every 3 years instead of every other year would still avert 1.6 deaths from breast cancer for every 1000 women screened.
Results were very similar in intermediate-risk women with scattered fibroglandular density, for whom 2 breast cancer deaths would be averted if women in this risk category were screened every 3 years compared with every other year.
In other words, 1000 women with fatty breasts or those with scattered fibroglandular density, both an indication of low breast density, and at intermediate risk for breast cancer would have between 6.4 and 7.2 fewer deaths from breast cancer if they underwent screening every 3 years instead of every 2 years.
The same group of women would have 471 to 734 fewer false-positive mammography results, the authors note, and 76 to 118 fewer benign biopsy results.
As Dr Trentham-Dietz and colleagues point out, the benefits of more frequent screening are more pronounced among women at intermediate risk for breast cancer but with increasing levels of breast density.
For example, for women at intermediate risk for breast cancer with heterogeneously dense breasts, rates of breast cancer deaths averted (10.6 per 1000 women screening) and false-positive mammograms (1125) were significantly in favor of biennial screening compared with no screening.
On the other hand, if the same category of women were screened annually rather than every other year, the false-positive rate would increase almost twofold relative to rates obtained with biennial screening, and death rates averted with annual vs biennial screening were not impressive, at 3.7 deaths per 1000 women screened.
Annual screening was most beneficial in the highest-risk women at all levels of breast density, in whom annual screening would avert 17.2 deaths in women with fatty breasts and 20.5 deaths in women with extremely dense breasts.
As investigators also note, screening mammography done every third year was the only cost-effective strategy for women at average risk for breast cancer and low breast density when considered against a quality-adjusted life-year threshold of $100,000.
"Biennial strategies were cost-effective for most density subgroups at average or intermediate risk," they add.
In contrast, screening every year was cost-effective only for women at intermediate or high risk for breast cancer with heterogeneously or extremely dense breasts.
"Women and providers understand that mammography may reduce the chance of late-stage breast cancer, which has a lower survival rate than if breast cancer is detected early," Dr Trentham-Dietz noted.
"However, women may not understand that mammography often leads to 'false alarms,' including false-positive mammograms, extra tests, and biopsies even when breast cancer is not present," she added.
"Tailored screening may reduce the chances that lower-risk women encounter these false alarms while increasing chances that higher-risk women have breast cancer detected early."
Reduce Breast Cancer Mortality
In an accompanying editorial, Christine Berg, MD, Johns Hopkins Medicine, Bethesda, Maryland, notes that the USPSTF recently confirmed that regular screening mammography helps reduce breast cancer mortality in women aged 40 to 74 years.
However, "[f]or any medical intervention, benefits need to be weighed against harms," Dr Berg writes, concurring with the authors.
"As we move toward more personalized medical interventions, tailoring one's recommendation based on individualized risk and individualized harm becomes increasingly important," she adds.
Dr Berg does question, however, how a woman or her physician can determine her risk level for breast cancer.
"The authors provide general guidance by listing published risk estimates for several factors such as age at menarche and menopause and a history of biopsy result of atypical hyperplasia," Dr Berg points out. (The BCSC Breast Cancer Risk Calculator is available at tools.bcsc-scc.org.)
However, Dr Berg still finds the necessary calculation of individual risk for breast cancer problematic and argues that further analyses are needed to determine whether benefits and harms prevail when women receive more sensitive types of breast imaging, such as MRI.
"This current work from the well-regarded Cancer Intervention and Surveillance Modeling Network and BCSC investigators helps women and clinicians to possibly individualize screening frequency based on risk and BI-RADS [breast density] categories," Dr Berg observes.
But "[i]t will be important to track outcomes in women who undergo alternative screening frequencies to validate this approach."
This work was supported by the National Institutes of Health. Dr Trentham-Dietz and Dr Berg have disclosed no relevant financial relationships.
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