Study examines impact of two-year screening interval for breast cancer

12/09/04

Except for women in their 40s, women who are screened with mammography every 2 years may not have an increased risk of late-stage breast cancer compared with women screened every year, according to a new study in the December 15 issue of the Journal of the National Cancer Institute.

The ideal interval between screenings for breast cancer using mammography has not been determined. In the United States, the U.S. Preventive Services Task Force recommends screening with mammography every 1 to 2 years, whereas the American Cancer Society recommends annual screening. In Europe, most countries recommend that women be screened every 2 years and concentrate their recommendations on women age 50 and older.

To determine if women screened every 2 years have an increased risk of late-stage breast cancer, Emily White, Ph.D., of the Fred Hutchinson Cancer Research Center in Seattle, and colleagues conducted an observational study using data collected by seven mammography registries in the United States. They examined whether the 2,440 women who had been diagnosed with breast cancer after receiving biennial screening were more likely to have been diagnosed with late-stage cancer compared with 5,400 women diagnosed with breast cancer after receiving annual screening.

Among women age 50 years or older, there was no increase in the risk of late-stage breast cancer for those who received screening every 2 years compared with those screened annually. There was also no indication that annual screening would benefit women with dense breasts. However, for women in their 40s, those who received biennial screening were more likely to have late-stage disease when they were diagnosed with breast cancer than were those who received annual mammograms (28% versus 21%).

"In summary, we found little evidence that indicates that women who undergo mammography screening every 2 years have an increased risk of late-stage breast cancer compared with women who undergo annual screening, except for women in their 40s," the authors write. "Our results may be useful for policy makers and for statistical modelers of mammography screening who seek to understand the costs and benefits of screening annually versus every 2 years."

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