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Getty ImagesWomen should have a mammogram every two years starting at age 50—not 40, according to an expert panels new breast cancer screening guidelines, which are sure to cause confusion among women, particularly those in their 40s who routinely schedule a mammogram each year.

However, a number of prominent groups say they strongly disagree with the new advice, which was issued by the U.S. Preventive Services Task Force (USPSTF) on Monday.

The USPSTF panel has backed off a 2002 statement advising women to have a routine mammogram every year or two beginning at age 40. The panel now recommends that women undergo mammography screening every two years starting at age 50 and continue being screened through age 74.

The USPSTF concluded that the benefit gained by starting screening at 40 versus 50 is “small” and that the decision to start screening before 50 should be an individual one.

The new guidelines would seem to reopen a debate that raged in the 1990s, but seemed to have been settled years ago. The American Cancer Society (ACS) now recommends that women get an annual mammogram and have a clinical breast examination beginning at age 40.

Otis W. Brawley, MD, the chief medical officer of the ACS, said in a statement that the ACS would stick to its current guidelines.

Mammograms are the “one screening test I recommend unequivocally, and would recommend to any woman 40 and over, be she a patient, a stranger, or a family member,” Dr. Brawley said. The USPSTF is an independent panel, sponsored by the federal Agency for Healthcare Research and Quality, whose members make recommendations about preventive-care services and published the new recommendations in the Annals of Internal Medicine.

The panels recommendations are based, in part, on a review of the latest scientific evidence on the benefits and harms of breast cancer screening. The pooled data show that mammography screening does reduce breast cancer death—by 15% for women ages 39 to 49. To prevent one cancer death in this group, 1,904 women would have to be screened. Among women 50 to 59, one death is avoided per 1,339 screenings.

Because breast cancer risk increases with age, younger women are at a somewhat lower risk of developing the disease, explains George W. Sledge Jr., MD, a professor of oncology at Indiana Universitys Melvin and Bren Simon Cancer Center, in Indianapolis, and president-elect of the American Society of Clinical Oncology.

Theyre also somewhat more likely to have a false-positive mammogram—a test result that triggers a biopsy or other tests, but turns out not to be cancer—because they tend to have denser breasts, he says.

“No one is saying, or no one should say, that screening mammography has no value for younger women,” he says.

What the task force is saying is that the absolute reduction in breast cancer deaths is much greater in an older population.

But the American Cancer Societys Dr. Brawley reasoned that “the USPSTF is essentially telling women that mammography at age 40 to 49 saves lives; just not enough of them.”

Next Page: Guidelines don't assess individual risk [ pagebreak ] The panel also considered data from a study using computer simulation models to compare expected outcomes of starting and stopping screening at different ages and screening at different intervals. The models suggest that screening average-risk women ages 50 to 74 every two years achieves most of the benefit of annual screening, but with less harm due to factors such as false-positive results, unnecessary biopsies, and “overdiagnosis” of cancers that wouldnt have progressed or would have not led to the persons death.

“[The models] only tell us what happens on average in the population. They do not tell us what will happen for an individual woman,” says Jeanne S. Mandelblatt, MD, the lead author of one of the studies commissioned by the USPSTF and a professor of oncology and medicine at Georgetown Universitys Lombardi Comprehensive Cancer Center.

For an individual woman, the decision to have a mammogram “is one that she needs to consider with her providers based on her risks and her values for the balance of harms and benefits,” she adds.

But W. Phil Evans, MD, the president of the Society of Breast Imaging, questions the wisdom of biennial screening. “It doesnt make any sense when you know more cancers can be found in the 50-year-old age group to lengthen the screening time, because the idea is to find the cancer early and to treat it while its small, because treatment can be less when the cancer is detected early,” says Dr. Evans, a professor of radiology and the associate vice president for clinical imaging services at the University of Texas Southwestern Medical Center, in Dallas.

“The Society of Breast Imaging and the American College of Radiology are not going to change their guidelines because of this,” he says. “We think its very important to begin screening at age 40 and screen yearly thereafter.”

The USPSTF panel did not make recommendations on screening women 75 and older because the current evidence is insufficient to weigh the additional benefits and harms. For the same reason, it did not weigh in on the value of clinical breast examinations, beyond mammography, in women 40 and older or on the value of other imaging techniques, such as digital mammography or magnetic resonance imaging.

However, it did recommend against teaching women how to perform breast self-examination, saying theres no evidence that it reduces breast cancer deaths.

The critical thing is not to ignore this lifesaving procedure, says Dr. Sledge, who urges all women to discuss mammography with their doctor, beginning at age 40.

“Whats not mentioned in these discussions, but whats incredibly important, is that in the United States, perhaps as many as even a third of all women just simply dont follow even the most conservative of screening mammogram recommendations, just as a significant portion of the population doesnt get screening for colorectal cancer or screening for cervical cancer,” Dr. Sledge notes.

“We could significantly reduce the number of cancer deaths if we applied even the most conservative of screening guidelines,” he says.

Breast cancer is the second-leading cause of cancer death in women, after lung cancer. In 2009, an estimated 254,650 breast cancer cases will be diagnosed, and 40,170 women will die from the disease.