For postmenopausal women with an average risk of breast cancer, a mammogram once every two years is a safe option, a new study suggests.
Published online in the Journal of the American Medical Association Oncology, the research also suggests that premenopausal women older than age 40 may decide to have an annual mammogram to increase their chances of finding cancers at an earlier stage. These women, should however, weigh this potential benefit against the increased potential for false alarms, which can occur more often with more frequent screening.
The findings help answer questions debated for many years: How often should women be screened, will some women benefit more from a shorter screening interval, and can others safely be screened less frequently?
For the study, researchers looked at 15,440 women between the ages of 40 and 85 who had been diagnosed with breast cancer within one year of an annual screening mammogram or within two years of a biennial screening mammogram. They defined annual mammograms as mammograms performed 11 to 14 months apart and defined biennial mammograms as mammograms performed 23 to 26 months apart.
They separated the women by age and by menopausal status, and among postmenopausal women, by whether they were using postmenopausal hormone therapy.
Premenopausal women diagnosed with invasive breast cancer after a biennial screening mammogram were more likely to have tumors with less favorable prognostic characteristics than women diagnosed after an annual screening mammogram.
“What was surprising is that based on previous studies we expected to see differences in breast cancer severity by screening interval among women 40-49 years of age and no differences by screening interval among women 50 years or older,” says Diana L. Miglioretti, professor of biostatistics at the University of California, Davis.
Instead, the differences found were based on the women’s menopausal status—not on their age.
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“For example, younger women were 17 percent more likely to have later-stage tumors if they were screened every two years versus annually, but that was not statistically significant. For premenopausal women, however, biennial screeners were 28 percent more likely to have later-stage tumors than annual screeners, which was statistically significant.”
Conversely, researchers found that postmenopausal women who were not using hormone therapy and were diagnosed as having breast cancer following a biennial or annual screen had similar proportions of tumors with less favorable prognostic characteristics. This was also true for women aged 50 and older.
“Our results suggest that menopausal status may be more important than age when determining screening intervals,” Miglioretti says. “They suggest that postmenopausal women may be safely screened every two years. In contrast, premenopausal women who are undergoing screening may want to be screened annually to increase their chances of diagnosing cancer at an early stage.”
Some women, such as those who have had their ovaries removed or are using certain types of birth control that result in not having periods, may not know their menopausal status. These women may want to base their screening decisions on their age instead. For example, the vast majority of women are postmenopausal by the time they are 55.
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To move toward a more personalized approach to screening, Miglioretti says future research should work to identify other risk factors that affect the benefits or harms of screening.
The research was conducted using data from the Breast Cancer Surveillance Consortium (BCSC), the United States’s largest collection of information on mammography, which consists of six breast imaging registries across the country. The American Cancer Society, which just published its new breast screening guidelines, used the consortium findings, as well as a review of existing evidence on screening mammography outcomes, to develop its new recommendations.
Coauthors of the study include researchers from the University of North Carolina at Chapel Hill, the University of Vermont, Dartmouth College, the American Cancer Society and University of California, San Francisco.
Source: UC Davis