Mammograms Benefit Women in their 40s, Study Shows

Mammograms catch tumors earlier, result in less invasive treatment and increase women's chances of survival. So, why shouldn't younger women be screened?

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Amidst the continuing debate over the age at which women should begin screening routinely for breast cancer, researchers report fresh evidence that women in their 40s whose cancers were picked up by mammograms need less treatment and live longer than cancer patients who were not screened.

The results focus on the very group — 40- to 49-year-olds — who were excluded in 2009 by the U.S. Preventive Services Task Force’s (USPSTF) revised breast-cancer screening recommendations. The expert panel, having weighed the life-saving benefits of routine mammography against its potential risks — including anxiety and unnecessary testing following false positive results and complications from unneeded biopsies and other procedures — concluded that routine breast cancer screening should begin at age 50 for most women. In younger women, the panel said, mammograms did more harm than good.

But based on the new data, researchers Judith Malmgren, Dr. Henry Kaplan and their colleagues at the Swedish Cancer Institute in Seattle argue that the USPSTF’s conclusions fail to consider key benefits of mammography: less invasive treatment and better outcomes for women whose cancers are detected early.

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Malmgren’s group studied 1,977 breast cancer patients aged 40 to 49, stratifying them by the stage of their disease, how their disease was diagnosed (by mammography or self- or physician-based exams), how it was treated and whether the cancer recurred. Over the 18-year study period, the percentage of breast cancers detected by mammography increased, from 28% in 1990 to 58% in 2008, due to increased screening. Over that same time period, the percentage of early stage tumors caught by mammograms increased as well — the number of Stage 0 cancers detected by screening jumped by 66%, while the number of more advanced Stage 3 cancers dropped by 66% as well.

When tumors were identified earlier, women were able to undergo less invasive treatments, with more using lumpectomy, or partial removal of breast tissue, and fewer having to resort to radical mastectomy, the removal of entire breasts. These early treatments translated into improved survival, with 4% of women whose cancers were detected by mammography dying of breast cancer compared with 11% whose cancers were not picked up by the screenings.

“Women are getting diagnosed earlier, when the cancer is at a more treatable phase,” says Malmgren. That might translate into a greater benefit for mammography than previous studies have shown. In the USPSTF’s analysis of screening’s benefits, Malmgren says the panel focused only on the number of lives saved by routine mammography. She argues that perhaps the panel should have also included benefits like less invasive treatment. Such benefits can be weighed more accurately against the risks of routine screening, including anxiety over false positive results and medical complications from unnecessary procedures.

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“The USPSTF says the harms outweigh the benefit, but if they don’t have all the benefits in the equation, then I don’t think it’s an accurate depiction of the situation,” Malmgren says.

She acknowledges that her study is an observational analysis, and cannot be used to recommend routine mammograms starting at age 40. But the findings justify that the definition of “benefits” should be broadened when balancing the pros and cons of regular breast-cancer screening in women aged 40 and 49. “I don’t think it’s prudent to throw the baby out with the bath water,” she says about the exclusion of this age group in national guidelines for routine screening. “We need to keep working out the issues.”

Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.