Miami, United States-In a controversial shift, a leading US medical association  urged women to wait until the age of 45 before getting an annual mammogram to screen for breast cancer.

The American Cancer Society previously recommended women be screened each year from age 40, but has changed its advice because evidence failed to show enough lives are being saved.

And while younger women are being advised to start later, women over 55 are now urged to switch to getting mammograms every two years, instead of annually.

"Since the last American Cancer Society (ACS) breast cancer screening update for average-risk women was published in 2003, new evidence has accumulated from long-term follow-up of randomized controlled trials and observational studies," said the guidelines, published in the Journal of the American Medical Association (JAMA).

Women should still have the opportunity to begin annual screenings at 40 if they choose, the guidelines noted.

Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital in New York, described the new guidelines as "disappointing."

"Although the recommendations are based on scientific studies, most of the studies only look at survival as the only important outcome," Bernik said.

"They fail to address the fact that women with smaller tumors often need less treatment." 

Breast cancer is the most common form of cancer in women worldwide. It is also the second deadliest form of the disease in women, after lung cancer. 

More than 40,000 women in the United States will die of breast cancer this year, according to background information in the article.

- Little benefit - 

Early detection can help improve survival, but screening all women beginning at age 40 can also lead to problems, such as false positives, biopsies, surgeries to remove masses that may not have been dangerous, and potential surgical complications, experts say.

Evidence from clinical trials has shown little benefit from mammograms when it comes to saving lives among younger women, said an accompanying editorial by Nancy Keating of Harvard Medical School and Lydia Pace of Brigham and Women's Hospital.

They wrote that regular mammography might prevent breast cancer deaths in about five of every 10,000 women in their 40s, or 10 of every 10,000 women in their 50s.

"Thus, about 85 percent of women in their 40s and 50s who die of breast cancer would have died regardless of mammography screening," they wrote.

Offering more sophisticated screening tests, including genomic risk factors, would be better for younger women than expanded screening mammography, they argued.

The new guidelines also no longer recommend breast exams, in which clinicians manually feel patients' breasts for lumps, for women of any age who do not have a family history of breast cancer.

The American Cancer Society cited the "absence of clear evidence" that they contribute "significantly to breast cancer detection prior to or after age 40."

The updated guidelines are now closer in line with the other major issuer of health guidelines, the US Preventive Services Task Force, which has already said that there is not enough evidence to support clinical breast exams as a way of finding breast cancer or preventing breast cancer deaths.

The ACS guidelines also urge older women to "continue screening mammography as long as their overall health is good and they have a life expectancy of 10 years or longer." 

Both groups recommend that screening decisions be individualized to reflect a woman's preferences and her underlying risk of breast cancer.

- Pre- or post-menopause - 

A separate study published in JAMA Oncology, which informed the American Cancer Society guidelines, found that women benefit more from yearly mammograms before they enter menopause.

"Our results suggest that menopausal status may be more important than age when determining screening intervals," said University of California, Davis researcher Diana Miglioretti.

"They suggest that postmenopausal women may be safely screened every two years. In contrast, premenopausal women who are undergoing screening may want to be screened annually to increase their chances of diagnosing cancer at an early stage."

According to Susan Boolbol, chief of the division of breast surgery at Mount Sinai Beth Israel, the problem is that many women are not aware of their personal risk.

"Another issue is that the overwhelming majority of women who develop breast cancer are average risk," said Boolbol, who was not involved in the writing of the guidelines.

"The main message is that women need to discuss these issues with their physicians and determine the best screening schedule for them."