Making informed decisions about mammograms

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.

So it’s a trade-off for women in their 40s?
Mammography is a trade-off for women of all ages, but for a long time mammography was not thought of in this way. Women got very strong, one-sided messages from doctors and advocacy groups, in essence telling them they were crazy if they didn’t get screened. Of course, this message isn’t true. Once informed about the chance of breast cancer and the benefits and harms of mammography, women can weigh the pros and cons. There is nothing crazy about encouraging women to make informed decisions based on their own values. But the only way this can happen is if women have the information they need.

How should doctors advise patients?
Doctors should help women realize that the issue is not whether mammography does or does not work. It’s about their values, how they weigh the benefits and harms. For so long, doctors have approached screening as something they have to convince women to do, even if this meant scaring people about their risk, exaggerating benefit and ignoring harms. The question is whether we are willing to be honest about both.
The panel took no position on insurance. But is money at issue?
The task force did not consider costs. It considered only the best available data. It would be better to focus on how much mammography helps and hurts first, without considering money, since bringing cost into the discussion distracts people. If you assume mammography works really well or has no downsides it is easy to assume that the debate is really about costs and rationing. But it isn’t. It’s about weighing benefits and harms. If a woman then decides she wants mammography, I do think insurance should cover it.

Does this outcry reflect a distrust of science?

It’s hard to know. Screening for breast cancer has been much more contentious than screening for other cancers. For example, when the same task force recommended against older men getting a PSA screening test for prostate cancer, there was little public reaction. Perhaps the difference is that prostate cancer affects older men or that many physicians, including urologists, have already adopted this practice. But the most important lesson is that people need better information. Too often the public get slogans about screening rather than good information. Slogans generate strong emotions that interfere with good decision making. By routinely hearing numbers about the benefits and harms of medical tests and treatments, people will be able to appreciate the science behind recommendations. It’s not about emotions. It’s about knowing what you get, and the trade-offs.