The American College of Physicians issued updated breast cancer screening guidelines recommending that average-risk women ages 50 to 74 receive a mammogram every other year. For women in their 40s and those 75 and older, the guidelines call for individualized discussions with a doctor rather than routine screening.

The guidelines apply to women at average risk who do not have possible cancer symptoms. For women aged 40 to 49, the guidance advises discussing the benefits and harms of mammograms with a doctor and, if screening is chosen, undergoing mammograms every other year. Doctors may also ask women aged 75 or older if they wish to stop routine mammogram screening.

"We're not saying there's no benefit from mammograms in the 40s, but there's a narrower balance between the benefits you could get and the harms in 40- to 49-year-olds." Dr. Carolyn Crandall said.

The recommendations differ from those of other major organizations. The U.S. Preventive Services Task Force recommends that average-risk women begin every-other-year mammograms at age 40 instead of 50. The American Cancer Society recommends that women aged 45 to 54 receive yearly mammograms and may choose to begin screening at age 40. For women aged 55 and older, the society advises they can switch to every-other-year mammograms or continue annual screenings, and states there is no reason for healthy women aged 75 or older to stop routine mammogram screenings.

More than 320,000 women in the United States will be diagnosed with breast cancer this year, according to the American Cancer Society. Breast cancer is the second-most common cause of cancer death in U.S. women, though death rates have been dropping for decades due to improved treatments.

Nearly half of women over 40 have dense breast tissue, which can make tumors harder to detect on a mammogram and can slightly increase breast cancer risk. Women are notified of their breast density after a mammogram. The American College of Physicians guidance advises considering digital breast tomosynthesis, also known as 3D mammography, for women with dense breasts.

"Breast cancer is not one disease. So how in the world does it make sense to screen everybody the same when everyone doesn't have the same risk?" Dr. Laura Esserman said. Esserman is leading research to better understand which women are at low, average, or high risk for breast cancer and to offer more tailored screening advice.