By Liz Szabo, USA TODAY
Up to 70,000 American women a year are treated unnecessarily for breast cancer because they were screened with mammograms, according to an analysis in today's New England Journal of Medicine that's likely to reignite a running debate over the value of cancer screening.
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The study, whose results are already being challenged by other cancer experts, finds that nearly one in three breast cancer patients - or 1.3 million women over the past three decades - have been treated for tumors that, although detectable with mammograms, would never have actually threatened their lives.
The study lays bare perhaps the greatest risk of cancer screening, called "overdiagnosis," long acknowledged by doctors and even advocates of mammograms, but unknown to most women who undergo the procedures.
Overdiagnosis occurs when technology detects cancers that, although technically malignant, behave as if they're benign, says study co-author H. Gilbert Welch of The Dartmouth Institute for Health Policy and Clinical Practice in Lebanon, N.H. Though it may surprise the average patient, Welch says, doctors have long known that some tumors aren't actually fatal. Instead, some remain dormant for years or even disappear on their own.
Doctors and public health campaigns typically emphasize the benefits of mammograms - such as the potential to detect cancers when they're smaller and more curable - but ignore the "huge human costs" of women who go through surgery, radiation and hormonal therapies for nothing, Welch says.
"We've suggested to women that having a mammogram is one of the most important things you can do for your health, and that's simply not true," Welch says. "I can't tell you the right thing to do, except to tell women the truth, tell them both sides of the story. We shouldn't be scaring women. This is a really close call."
Though policy experts are familiar with such tradeoffs, few others understand that, in any screening program, some women will be harmed while others are helped, says Fran Visco, president of the National Breast Cancer Coalition. Breast cancer therapies can be very toxic, leading to second cancers, heart failure and even death, Visco says.
"When you intervene in a healthy population, you better be sure you're helping them, because you can be sure you're harming them," says Visco, a breast cancer survivor, who wasn't involved in the new study. "If it were really clear mammograms saved a lot of lives, there wouldn't be this constant debate."
Many cancer survivors credit mammograms with saving their lives, a conviction that can help sustain them through painful treatments.
Authors acknowledge their paper doesn't offer any guidance to women diagnosed with cancer. Because doctors can't tell for sure which tumors are most dangerous, they treat all breast cancers - and even pre-cancers - as if they have the potential to kill, says co-author Archie Bleyer of St. Charles Health System in Bend, Ore.
Cancer advocates had mixed reactions to the analysis. Some say the authors overestimate the problem of unnecessary treatment.
In a statement, the American Cancer Society says "overdiagnosis is a matter deserving of attention," but it notes that other analyses have arrived at different estimates of the number of patients treated unnecessarily.
Len Lichtenfeld, the society's deputy chief medical officer, urged people to view the findings "with caution."
Overall, "the benefits of screening mammography outweigh the risks and harms, which are an unavoidable part of breast cancer screening," Lichtenfeld says.
Rigorously designed clinical trials - the gold standard of medical evidence - have found that mammograms reduce the death rate from breast cancer by about 15% in women in their 40s and 50s and 30% for women in their 60s. More recent studies, though less rigorously designed, suggest the benefits could be even greater, says radiologist Barbara Monsees, speaking for the American College of Radiology.
"We know that overdiagnosis exists," Monsees says. Although doctors need better tools to differentiate lethal tumors from relatively harmless ones, Monsees says, "we should continue to screen, because we know we can save lives."
Eric Winer, head of breast medical oncology at Boston's Dana-Farber Cancer Institute, notes that the study found an 8% reduction in the number of women whose tumors were detected at more advanced stages. Even under a scenario in which mammograms led more than 1 million women to receive unnecessary treatment, the screenings would have prevented 410,000 diagnoses of late-stage cancer.
While researchers struggle with these issues, Winer says, women often hear a much more simplified message.
"We probably have to some degree oversold the benefits of mammography, but we still know that mammography is beneficial, certainly for women over the age of 50 and likely for some women under 50," Winer says. "I don't think we need to abandon mammography. It's still our best test, although we desperately need better tests."
Experts offer different recommendations about the frequency and timing of mammograms. The American College of Radiology and American Cancer Society both recommend women get annual mammograms beginning at age 40. The U.S. Preventive Services Task Force recommends that women be screened every other year beginning at age 50, but they should make up their own minds about whether or not to have mammograms before that.
Given the test's limitations, Winer says, women may choose to have fewer screenings to reduce their risk. "It certainly suggests that a woman who chooses to wait until she's 50 to have mammograms, or who chooses to have mammograms every other year, is making a rational decision," Winer says.
Barry Kramer, director of the National Cancer Institute's division of cancer prevention, says women should be presented with the full picture of mammography's risks and benefits.
Though women have been instructed that "early detection saves lives," relatively few are told that screenings also have costs, including the risk of undergoing surgery, radiation and drug therapy that doesn't help them, Kramer says. "The risks of overdiagnosis are real, and women ought to know about it," Kramer says.