In November, the U.S. Preventive Services Task Force, a nongovernmental advisory panel of health experts, recommended that routine mammography for breast cancer screening start at age 50, not 40. It met with a chorus of objections. Lisa Schwartz, a general internist at the Dartmouth Institute for Health Policy and Clinical Practice in Lebanon, N.H., investigates such public health issues. She spoke recently with Science News biomedical writer Nathan Seppa.
Were you surprised at the outcry that arose from this recommendation?
Yes and no. This happened in 1997 when a National Institutes of Health consensus panel recommended that women in their 40s decide for themselves about mammography: an intensely negative public and political reaction. But I also hoped that with the growing acknowledgment of the harms of mammography — in medical journals, in the news and by the head of the American Cancer Society — that there might have been a different reaction.
Mammograms do catch cancers. But the task force found high rates of false-positive mammograms and treatment for “overdiagnosed” cancer, questioning the benefits of routine mammography for 40-somethings. Your thoughts?
Women need to be clear about their chance of developing breast cancer, how much mammography reduces that chance and what are its associated harms. Imagine 10,000 women age 40. Over the next 10 years, without mammogram screening, about 35 will die of breast cancer. With screening, 30 will die — five fewer. But of 10,000 getting screened, 600 to 2,000 will have at least one false positive leading to a biopsy, and 10 to 50 will be overdiagnosed. They will be told they have cancer, and they will undergo surgery, chemotherapy or radiation, which can only hurt them since their cancer was never destined to cause symptoms or death.
Overdiagnosis is the most important harm of screening. People sometimes find it hard to believe that overdiagnosis is possible. These cancers look the same under the microscope but don’t behave like cancer. Because we can’t tell which cancers constitute an overdiagnosis, everybody who has cancer is treated.