Nearly 270,000 American women are expected to be diagnosed with breast cancer this year, and 65 percent of women 40 and over have had a screening in the past two years. But there's been conflicting guidance on how often women should get mammograms.

The American Cancer Society recommends women age 45 to 54 with an average risk of breast cancer get a mammogram every year. Then starting at 55, every other year.

But on Monday, the American College of Physicians (ACP) said for some women, it should be less frequent. It recommends the majority of women get a mammogram every other year beginning at age 50 and younger women should speak to their doctors about the benefits. There are exceptions, like for women who have had a prior abnormal screening, a previous diagnosis of breast cancer, or a genetic mutation known to increase risk.

The ACP says evidence shows annual mammograms can lead to more harm, such as anxiety over false positives and unnecessary testing. Annual mammograms versus bi-annual results show no significant difference in the breast cancer death rate.

The new guidelines were meant to provide clarity to existing and sometimes conflicting screening recommendations. The ACP also said doctors should not use clinical breast exams to screen for breast cancer.