Endless Screenings Don’t Bring Everlasting Health
This month, nine major medical specialty groups published a list of 45 tests and procedures that often have no clear benefit for patients and can cause harm — CT scans for simple headaches, for example, and X-rays for routine lower back pain. You don’t often hear calls from doctors for fewer tests and procedures.
And that’s too bad. Many of them have been oversold, their benefits exaggerated and their harms ignored.
Consider cancer screening. For decades, it has been nearly impossible to watch television, read popular magazines or ride public transportation without seeing advertisements urging regular mammograms, colonoscopies or P.S.A. blood tests. These messages have had a profound effect: the public is now extremely enthusiastic about the notion that we should routinely screen people without symptoms for cancer. In one national survey, most Americans said that cancer screening is almost always a good idea and that finding cancer early saves lives most of the time.
Certainly, the rationale behind screening seems obvious. The earlier cancers are diagnosed, the more often lives will be saved, right? With enough screening, we might even stop cancer.
If only. Finding cancer early isn’t enough. To reduce cancer deaths, treatment must work, yet it doesn’t always. Second, it must work better when started earlier. But for some cancers, later treatment works as well. (That’s why there is no big push for testicular cancer screening — it is usually curable at any stage.)
And some of the worst cancers aren’t detected by screening. They appear suddenly, between regular screenings, and are difficult to treat because they are so aggressive.
So how can we be confident that getting a screening test regularly is a good idea? The only way to be sure is to look at the results of randomized trials comparing cancer deaths in screened and unscreened people. Even when screening “works” in such trials, the size of the benefit observed is surprisingly low: Generally, regular screening reduces fatalities from various cancers between 15 percent and 25 percent.
What does that mean? Think about a “20 percent off” sale at a store. Whether you save a lot or a little depends on the item’s regular price. You’ll get huge savings on a diamond ring, pennies on a pack of gum.
The benefit of screening is like a sale, only you don’t save money — you “save” on your chance of dying. Whether you save a lot or a little depends on the “regular price”: your chance of dying without screening.
For most of us, the chance of dying of cancer in a given 10-year period is small: less than 1 percent. So regular screening with a proven test may bring a 20 percent reduction in a 1 percent risk over a decade. Put another way, two deaths would be prevented for every 1,000 people screened during that period.
And what of the other 998 whose fate was not changed by screening? Some of them will have been harmed.
The most familiar harm is a false alarm: The screening test is abnormal, but in the end there is no cancer. False alarms matter because the follow-up tests needed to rule out cancer can be painful, dangerous and scary.
But overdiagnosis — the detection of cancers never destined to cause problems — is arguably the most important harm of screening. Some cancers grow so slowly that they would never cause symptoms or death. When screening finds these cancers, it turns people into patients unnecessarily.