For years, it has been hammered into our brains that the best way to prevent deaths from breast cancer was to find it as early as possible and treat it right away. That led to a set of recommendations for routine mammography screenings, and that in turn led to a lot of breast cancer being discovered while it was still highly treatable. All good things, to be sure. But now it seems we're finding breast cancer too early.
A new study appearing in today's Annals of Internal Medicine has found that between 15 and 25 percent of breast cancers discovered by mammograms would not have caused a woman any problems during her lifetime. This problem is known as "overdiagnosis," a strange term, which Dr. Otis Brawley, chief medical officer of the American Cancer Society, explained to CNN in this helpful way:
[I]t refers to a tumor that fulfills all laboratory criteria to be called cancer but, if left alone, would never cause harm. This is a tumor that will not continue to grow, spread and kill. It is a tumor that can be cured with treatment but does not need to be treated and/or cured.
Overdiagnosis has already been seen in treating prostate cancer and to some extent in thyroid, lung, and other cancers. In the case of breast cancer, because we can't yet tell which types of the cancer spread and kill and which don't, we need to treat any tumor that's found as if it's deadly. That means surgical removal and sometimes radiation or chemotherapy.
There have been other studies that looked at the phenomenon of overdiagnosis, but estimates of how prevalent a problem it is have varied. This new study is particularly robust because it used data collected in Norway during the introduction of a screening program that took place over the course of a decade. This allowed researchers to compare breast cancers from counties where screenings were offered against places where they weren't yet offered. Researchers ended up analyzing some 40,000 breast cancer cases in total, including 7,793 cases where cancer was detected after routine screenings started. They found that between 1,169 and 1,948 of those women were overdiagnosed and received unnecessary treatments. Because Norway offers women screenings every two years between the ages of 50 to 69, it's estimated that the number of overdiagnosed cases would actually be even higher in the U.S., where we begin routinely screening women at 40 instead of 50.
So what exactly are we supposed to do about this? Well, mainly just be informed, which is medicalese for "be freaked out with no way to help yourself." It's clearly a problem, but there is no clear solution. If you take a more macro view, theoretically we ought to stop screening women so early (unless they have a family history of breast cancer), and we ought to be less aggressive in treating certain breast cancers. But that idea obviously becomes problematic when you try to practice caution on any given individual. Back in 2009, when a task force made the bold suggestion that we not start routine mammography until age 50, people went nuts. Some with good reason: they had a mother, sister, aunt, friend, grocery cashier, etc. whose life had been saved because of a mammography before 40. And, of course, there are many cases where early screening is an actual life saver, but for all of those cases there are these other cases of women being overdiagnosed and getting unnecessary surgery or chemotherapy, which is a highly undesirable medical outcome too.