The American Cancer Society recommended Tuesday that women move away from the early and frequent mammograms that have been standard practice in the United States for nearly two decades.

The new guidelines call for women to begin getting annual mammograms at age 45, rather than at 40, as the group had previously recommended. At 55, the age used as a proxy for menopause, women should transition to having mammograms every other year, and continue as long as they are healthy and expect to live at least 10 years, according to the new recommendations.

In another major change, the American Cancer Society recommended against the six-minute clinical breast exam – in which a doctor physically checks for lumps – for women of any age.

The latest guidelines, which apply to women of average risk, reflect a growing concern that the benefits of the test may have been oversold and that overdiagnosis and false positives are resulting in unnecessary anxiety and costly treatments.

Still, the change upset some patient advocates and was especially striking because the cancer society in the past has sharply disagreed with groups recommending a scale-back of mammograms. In 2009, it criticized a federally appointed group, the U.S. Preventive Services Task Force, for recommending that women start regular testing at age 50.

But now, after examining years of additional research, the cancer society has moved in that direction. The guidelines were published Tuesday in the Journal of the American Medical Association.

Richard Wender, a former president of the American Cancer Society and a member of the group’s breast cancer guidelines panel, said that the new recommendations, while confirming that mammography is the most important thing a woman can do to reduce her chance of dying from breast cancer, also are designed to provide a more “personalized and tailored approach.”

“Over the past couple of years, there has been so much confusion that some women and some clinicians have really lost confidence in mammography,” he said. ” We hope this extraordinary and thorough review will calm that worry.”

The recommendations, which are for women who don’t have specific risk factors such as mutations of the BRCA1 and BRCA2 genes or a family history of the disease, are not binding on doctors, hospitals, insurers or individuals. Indeed, the cancer society noted that women should still “have the opportunity” to get mammograms if they wish.

Still, some breast cancer patient groups expressed alarm that the guidelines may prompt some women to skip life-saving screenings and provide health plans with an excuse to stop covering the tests in some circumstances.

“We are worried about the message and confusion to the public when they see these new guidelines. The cutback on screening is falsely reassuring,” said Marisa C. Weiss, an M.D. who is the founder and president of Breastcancer.org.

Judy Salerno, president and CEO of Susan G. Komen, said she was concerned that the new guidelines “have the potential to lead to reduced accessibility to and coverage for health screenings from both private and public insurers.”

The ACS’s updates come as cancer experts are rethinking the very definition of cancer. Thanks to advances in genetic testing, blood-based markers and digital imaging, cancer is being diagnosed earlier than ever and there’s a new recognition that there is a subset of tumors that may never grow enough to be harmful to a patient. The most obvious example involves prostate cancer but researchers have found similar cases in other types of cancers.

Mammograms, which have been used for more than a century to pinpoint irregularities in breast tissue, are credited with saving many millions of lives by catching cancers at their earliest stages. Breast cancer is one of the leading killers of women in the United States; 225,000 are diagnosed with the disease each year and 41,000 die.

Many women have come to believe that the more screening and the more treatment the better – in part because of the message conveyed by breast cancer fundraisers with ubiquitous pink ribbons and in part because of stories like Angelina Jolie’s.

But a number of new studies have questioned this idea.

As recently as August, a study in JAMA Oncology found that the overall risk of dying after being diagnosed with so-called stage 0 – or ductal carcinoma in situ – cancer was 3.3 percent overtwo decades and that pursuing treatment beyond a lumpectomy did not affect survival.

The American Cancer Society is one of a small number of organizations whose recommendations have a big influence over how doctors treat their patients – and now those groups are recommending three different ages when regular breast cancer screening should begin.

The American College of Obstetricians and Gynecologists recommends that regular screenings begin at age 40. The U.S. Preventive Services Task Force reaffirmed its view in April that women between ages 50 and 74 get routine screening once every two years.

ACOG said that it will convene a conference that will include ACS in January with the goal of creating a consistent set of uniform guidelines for breast cancer screenings.

Nancy L. Keating, a doctor in internal medicine and primary care at Brigham and Women’s Hospital who wrote an editorial in JAMA, formerly the Journal of the American Medical Association, accompanying the new guidelines, said the discrepancy shows how controversial the subject of mammograms can be.

“If there were an easy answer they would all have the same conclusions,” she said in an interview.

Daniel Kopans, a professor of radiology at Harvard Medical School, noted that the American Cancer Society, in explaining its updates, cited the “emotional effects” of being called in to undergo more testing after a mammogram produces ambiguous results.

“They seem to have wanted to account for the inconvenience of a recall from screening to suggest that some women might prefer to chance an avoidable death for a reduced chance of being recalled for a few extra pictures or an ultrasound,” he said.

Breastcancer.org’s Weiss said she was concerned that being “average” or “high” risk is poorly understood and can change over time.

Both she and Kopans said they will not change the advice they give their patients on mammograms based on the new guidelines. They pointed out that both the ACS and the federal preventive-services task force agree that the most lives are saved by annual screenings that start at age 40.

“I support the science which is every year starting at age 40,” Kopans said. “This is my recommendation.”