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When to Get a Screening Mammogram

How often and when to start routine mammograms is a matter of debate.

The Trouble With Statistics

The argument over when women should start breast cancer screening stems from a disagreement about the process the task force used to reach its conclusions. It relied on a sophisticated computer model rather than real-life, clinical, randomized studies to determine how many breast cancers are caught and treated in women ages 40-49.

Lichtenfeld says that the conclusions reached by multiple institutions using the same model were different. "So the reliability of that model to make a clinical decision, particularly when we have data from actual studies, we felt was not quite ready for prime time," he says.

Phil Evans, MD, representative of the Society of Breast Imaging and director of the Center for Breast Care at the University of Texas Southwestern Medical Center, concurs with Lichtenfeld.

"One of the assumptions the task force made was the reduction of mortality in between the ages of 40 and 49 was 15%, and we know from real-life studies ... that the number is closer to 30%, twice what they used in their modeling. That's a huge difference in the number of lives saved," he says.

"The task force did acknowledge at the time that mammography did reduce deaths for women between ages 40-49, Lichtenfeld says. "However, we said then, and I think it's fair to repeat today, that the task force didn't feel enough lives were saved for women in that age group, because breast cancer is more common as you get older." 

The American Cancer Society, Lichtenfeld says, disagrees and continues to recommend routine screening mammograms for women age 40 and older.

The Harm of Too Much Testing

One of the central issues upon which the USPSTF based its recommendations had to do with the harm that can come from mammography testing: psychological harm, unnecessary imaging tests and biopsies, and false-positive mammogram results in which the patient is told there could be cancer, when in fact none exists. False-positive results are more common for women aged 40 to 49 than for older women.

"They were saying they felt the risk of harm of having extra procedures outweighed the benefit from saving lives, " Lichtenfeld says of the Task Force's reasoning to delay mammography.

The fact is that as women age, false positive mammography results decline. That's mainly because the density of a woman's breasts tends to decrease with age, making it easier to find cancer.

"Any given test that is a positive is more likely to be [truly] positive as women get older," Petitti says. A woman in her 40s asked to come back for follow-up tests because of a positive mammography has a 1 in 10 chance of actually having cancer.

But experts say that women understand mammography has limitations and still want to be screened for breast cancer.

"Most of the women you talk to would much rather go through that process and find something early than wait, " Evans says. "No one likes to have a false positive about anything, but it's part of what has to be done to find breast cancer early."

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