HealthDay News — The benefits of starting breast cancer screening at age 40 years for women with extremely dense breasts or a family history of the disease may outweigh the risks, results from two studies suggest.

Biennial screening mammography for these two groups had the same ratio of false-positive risk to life-years gained benefit as for average-risk women that begin screening at age 50, Nicolien T. van Ravesteyn, MSc, of Erasmus Medical Center in Rotterdam, the Netherlands, and colleagues, reported.

In a jointly conducted meta-analysis that involved 66 studies, Heidi D. Nelson, MD, MPH, from the Oregon Health & Science University in Portland, and colleagues found women aged 40 to 49 years who had extremely dense breasts (Breast Imaging Reporting and Data System [BI-RADS] category 4) or first-degree relatives with breast cancer, had a twofold increased risk breast cancer. Both studies appeared in the May 1 issue of the Annals of Internal Medicine.

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Approximately 9% of U.S. women have a first degree relative with breast cancer and 13% have BI-RAD category 4 breast density, according to study background data.

“Results of these two studies imply that women with these characteristics could benefit from biennial screening starting at age 40 years,” van Ravensteyn et al wrote. 

The debate over when breast cancer screening should begin started in 2009, when the U.S. Preventive Services Task Force recommended no routine mammography before age 50 years based on high false-positive rates in younger women.

In an editorial accompanying the two studies, Otis W. Brawley, MD, of the American Cancer Society in Atlanta, suggested that risk-based screening guidelines — although potentially more difficult for health-care providers to implement — may be the best way to detect the life-threatening disease while minimizing necessary use of healthcare resources.

“If screening efforts could focus on women at greatest risk for breast cancer, the number of women harmed would decrease and the number benefiting would increase,” Brawley explained.

Using this strategy very high risk women would get screened annually, whereas those at intermediate risk would undergo biennial screening and those at normal risk would start screening later.

Van Ravesteyn’s group built a model based on data from the Surveillance, Epidemiology, and End Results (SEER) program, the Breast Cancer Surveillance Consortium, and other sources to assess the  risks and benefits of screening at different age ranges. They found that biennially screening women aged 50 to 74 years would result in 6.3 breast cancer deaths averted per 1,000 women, 109 life-years gained and 883 false-positives.

For women in their 40s to reach the same ratio of 8.3 for false-positives to life-years gained, they would have to be at a minimum 1.9-fold elevated relative risk for breast cancer, the researchers found. However, annual screening and digital mammography were associated with more harm in terms of false-positives.

In the meta-analysis, Nelson and colleagues, found that the following characteristics substantially elevated breast cancer risk as follows:

  • First-degree relatives with breast cancer resulted in a relative risk (RR) of 2.14 for one relative, 3.84 for two, and 12.05 for three or more
  • Relatives with breast cancer at a young age resulted in a RR of 3.0 before age 40 years
  • Dense breasts increased the RR to 1.62 for BI-RADS category 3, and 2.04 for category 4 vs. category 2
  • Prior benign results on breast biopsy resulted in a 1.87 RR

“Identification of these risk factors may be useful for personalized mammography screening,” Nelson’s group wrote.

Other statistically significant but lesser contributing risk factors were not having given birth to any children (RR=1.16; 95% CI:1.04-1.26) or a first child at age 30 or older (RR=1.20; 95% CI:1.02-1.42). Furthermore, additional findings from an analysis of prospective data from the Breast Cancer Study Consortium suggest that taking oral contraceptives may also increase the risk for breast cancer (RR=1.30 vs. former or never use; 95% CI: 1.13-1.49).

“A potential difficulty with including breast density in screening recommendations is that breast density is not uniformly reported and requires baseline mammography examinations to determine breast density, introducing additional potential screening harms,” van Ravesteyn’s group added.

Van Ravesteyn NT et al. Ann Intern Med. 2012;156(9):609-617.

Nelson HD et al. Ann Intern Med. 2012;156(9):635-648.

Brawley OW. Ann Intern Med. 2012;156(9):662-663.