Washington ? The nation’s largest medical specialty group is challenging the widely accepted recommendation that women should routinely undergo mammograms in their 40s, saying the risks of the breast exams may outweigh the benefit for many women.

Reopening a long-running debate, the American College of Physicians, which represents 120,000 internists, plans to issue new guidelines today that instead urge women in their 40s to consult with their doctors individually about whether to get the breast X-rays.

The group based its recommendations on a comprehensive review of research on mammography that concluded the benefit is less clear for women in their 40s than for those 50 and older, and that screening carries significant risks, including exposure to radiation and unnecessary biopsies, surgery and chemotherapy.

The guidelines conflict with long-standing recommendations from several other leading medical groups, including the American Cancer Society and National Cancer Institute.

“We agree that mammography can save lives,” said Douglas Owens of Stanford University, chairman of the committee that wrote the guidelines being published in the Annals of Internal Medicine. “But there are also potential harms. We don’t think the evidence supports a blanket recommendation.”

The new guidelines elicited mixed reactions from breast cancer advocates, doctors and researchers. Some condemned them, saying mammograms clearly help catch tumors at their earliest, most treatable stage, reducing the death toll from the common malignancy. Breast cancer tends to be especially deadly when it strikes women in their 40s, they noted.

“The danger here is that some women will elect not to get screened,” said Robert A. Smith, director of cancer screening at the American Cancer Society. “Mammography is the single most effective way of finding breast cancer early, and when we find breast cancer early women have the greatest chance of successful treatment.”

But others said the recommendations represent a more nuanced approach that better reflects what is known about the benefits and drawbacks of mammography.

“I think it’s right on target,” said Russell Harris of the U.S. Preventive Services Task Force, which issues the federal government’s official recommendations on preventive medicine. “I would like to see more women stop and think about the decision.”

The new guidelines come less than a week after the Cancer Society issued new guidelines that, for the first time, recommend that women at greatest risk for breast cancer also undergo annual MRI exams. That statement triggered a similar debate over the risks and benefits of aggressive screening.