April 20--An expert panel convened by the federal government is standing by its controversial recommendation that most women should get mammograms to check for signs of breast cancer only once every two years, and that the tests need not begin until the age of 50.
The draft report from the U.S. Preventive Services Task Force reiterates that mammograms do indeed save lives. But it also emphasizes the test's downsides, many of which are unappreciated by doctors and the general public.
Chief among the problems associated with screening mammography is the risk that it will result in unnecessary procedures and treatment by finding abnormal cells that would have been harmless if left alone, according to the panel, which first raised questions about the test in 2009.
"About one out of every five women diagnosed by screening mammography and treated for breast cancer is being treated for cancer that would never have been discovered or caused her health problems in the absence of screening," according to the report released Monday.
Breast cancer is the second-leading cause of cancer death among women in the U.S., after lung cancer. Among every 10,000 women in the U.S., about 125 are diagnosed with breast cancer each year and 22 die of the disease. That translated to about 233,000 new diagnoses and 40,000 deaths in 2013.
No wonder, then, that women eager to stay healthy have embraced mammograms. Two-thirds of American women ages 40 and above said they've had the test within the last two years, including 51% who had it within the last 12 months, according to the American Cancer Society.
Several groups -- including the American Cancer Society, the National Comprehensive Cancer Network and the American College of Radiology -- continue to recommend annual mammograms for women at average risk of breast cancer beginning at age 40.
But the task force reiterated its advice that most women get tested only once every two years, and that the test is most effective for women between the ages of 50 and 74.
"Age is the most important risk factor for breast cancer," the panel wrote.
For instance, if 10,000 women in their 60s were screened for a decade, the result would be 21 fewer deaths due to breast cancer, according to data from clinical trials. Among women in their 50s, the same amount of screening would avert eight breast cancer deaths.
Against those benefits, the experts considered the costs of treating breast tumors that are revealed by mammograms but aren't dangerous. They also factored in the unnecessary procedures brought on by false-positive test results as well as the small but real number of breast cancers that are caused by the radiation in mammograms.
Overall, the panel determined "the net benefit of screening mammography in women ages 50 to 74 is moderate."
But for most women in their 40s, the net benefit of screening is too small to warrant a blanket recommendation in its favor, the panel determined.
"Women ages 40 to 49 must weigh a very important but infrequent benefit (small reduction in breast cancer deaths) against a group of meaningful and much more common harms," according to the report. These harms include "overdiagnosis and overtreatment; unnecessary and sometimes invasive followup testing and psychological harms associated with false-positive tests; and false reassurance from false-negative tests."
However, if women in this age group have a first-degree relative -- a mother or sister -- who has been diagnosed with breast cancer, their own risk of the disease is comparable to that of a typical woman in her 50s. As a result, biannual screening for these women makes sense, the panel wrote.
Researchers have not conducted clinical trials to test the value of screening mammograms among women over the age of 70. Mathematical models indicate the tests can be useful for women between the ages of 70 and 74. Beyond that, the data needed to endorse the test for older women is "insufficient," the panel wrote.
All of these recommendations are in line with those made in 2009.
