By Tony Pugh

A new report estimates that 17 million women ages 40 to 49 could lose free annual mammogram coverage if an influential medical panel adopts its proposed breast cancer screening guidelines.

The new figures are the latest development in a growing medical and political controversy that was resurrected last month after Congress quashed it in 2010.

The Affordable Care Act requires many health plans to cover certain preventive services at no cost to patients if the procedures receive A or B grades from the U.S. Preventive Services Task Force, an independent group of experts in prevention and evidence-based medicine.

The task force assigns the letter grades A, B, C and D based on the strength of evidence, the benefits and the harm of preventive services.

In November 2009, the task force sparked a major controversy by recommending that mammograms for women ages 40-49 receive a C grade.

There's no clear consensus on the issue. Many cancer societies recommend annual mammograms for women 40 and over, for example.

Opposition to the task force's 2009 recommendation from the Obama administration, members of Congress and several medical organizations resulted in the health law requiring that the Department of Health and Human Services ignore the task force's recommendation and follow screening guidelines that were "the most current other than those issued in or around November 2009."

That stipulation allowed breast cancer screening under the health care law to be guided by the task force's 2002 recommendation, which gave mammograms for women 40 and older a B grade, thus allowing for insurance coverage at no cost to patients.

Last month, however, the task force revived the debate by issuing a draft recommendation that again put a C grade on breast-cancer screening for women ages 40 to 49. If the proposal is finalized, health plans would no longer have to fully cover mammograms for women in this age group although they could choose to do so.

"The science shows that some women in their 40s will benefit from mammography, most will not, while others will be harmed," the task force statement said. The most serious harm is "unneeded diagnosis and treatment for a type of breast cancer that would not have become a threat to a woman's health during her lifetime," while the most common harm is a false positive test result, "which often leads to additional tests and procedures."

The task force said mammography screenings every two years were most beneficial for women ages 50 to 74. It urged women in their 40s to make breast cancer screening decisions in partnership with their doctors based on their own values, preferences and health history.