“I am discussing it. I’m telling you to get a mammogram,” she replied. When I asked her why, she told me because it could save my life.
What she neglected to tell me is that a mammogram was, in my case, more likely to hurt than help me. Few doctors take the time to mention the risks of mammography — especially, the danger of overdiagnosis — that a
mammogram might lead a patient to get needled, sliced, zapped with radiation and possibly treated with tamoxifen, a drug that increases risk of uterine cancer, for a breast lesion that wasn’t life-threatening in the first place.
Most people believe that breast cancer is inevitably a progressive disease that will kill you if you don’t remove it in time. According to this idea, which I call the relentless progression model, every big cancer is harmful, every small one is less so and every cancer is curable if only you catch it in time. It’s an appealing, intuitive idea — except that a growing body of research suggests that it’s wrong.
Scientists now know that breast cancers can behave in different ways. The disease falls into three general behavioral categories, according to Barnett Kramer, director of the National Cancer Institute’s Division of Cancer Prevention. Kramer refers to the three types as turtles, birds and bears.
Turtles are cancers that progress so slowly that they will never metastasize or harm you. Finding these cancers won’t save your life, because they never endangered it in the first place, Kramer says. Birds, on the other hand, are extremely aggressive cancers that are programmed to become deadly. These cancers aren’t helped by mammography, either, because they spread before they can be detected on a mammogram.
It’s only the bears whose future is altered by mammography, Kramer says. Bears may eventually kill you if they’re not treated, but they spread slowly enough that a mammogram can detect them in time to make a difference.
Here’s the problem: At the moment, we don’t have a reliable way to distinguish turtles, birds and bears. While scientists are working to find genetic markers that predict how a cancer will behave, right now the only way to know which way a cancer will act is to wait and see what it does. This means that if a mammogram finds a breast cancer, the safest course of action is to assume that it’s a bear. This inevitably leads to some women with turtles and birds receiving treatment that doesn’t help.
Those with turtles end up getting treated for cancers that were never destined to cause any harm. Women who have such cancers are grateful because they believe their lives have been saved. Their doctors and radiologists become even more convinced that mammography saves lives. In fact, these women are victims of overdiagnosis.