By Alexandra Sifferlin
October 22, 2015

For the first time in 32 years, the American Cancer Society (ACS) has changed the age at which it recommends women start getting regular mammograms. The ACS now advises that women at an average risk for breast cancer begin yearly screening at age 45–it had previously recommended starting at 40–and to transition at age 55 to a schedule of every other year.

The new recommendations, which represent a more personalized approach to the question of who needs screening when, are the result of an ACS evidence review that was published Oct. 20 in the journal JAMA. While the new guidelines advise every-other-year for women over 55, the ACS also emphasizes that women should have the option of sticking with an annual schedule if they choose. Women should also have the option to begin regular screening at 40, the report says.

The ACS says its guidelines were due for an update; the group’s most recent recommendations are 12 years old. “In 2003 nobody talked about the balance of benefits and harms, which is now really a standard for guidelines,” says Dr. Richard Wender, chief of cancer control at the ACS.

One of the drawbacks of screening is false positives: over 10 years, a woman receiving an annual mammogram has a 61% chance of getting such erroneous results. Another is mounting evidence that aggressive treatment of some early-stage cancers is unnecessary and can have lifelong side effects.

The new guidance may clear up some confusion around when–and how often–women should get mammograms. In 2009, the U.S. Preventive Services Task Force said there was insufficient evidence to support the recommendation that women start at 40, and it changed its official advice to biennial screening beginning at 50 for most women. Until now, the ACS continued to recommend a starting age of 40.

“The evidence simply no longer supports one-size-fits-all,” says Dr. Kevin Oeffinger, chair of the ACS breast-cancer-guideline committee. “In medicine we are moving closer and closer to bringing about a personalized approach.”

Contact us at editors@time.com.

This appears in the November 02, 2015 issue of TIME.

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