By Regina Nuzzo
Cancer Screening Conundrum
Overdiagnosis can lead to unnecessary and risky treatment
By Regina Nuzzo
The idea of an annual cancer screening test makes perfect sense: Find cancer early and treat it before it becomes dangerous.
Yet, over the past two years we’ve seen updated guidelines suggesting that some women and men may actually be getting too much screening for cervical, prostate and breast cancer. It seems counterintuitive. When it comes to cancer, how can you be too cautious?
What has changed is that as more people have gotten more screening tests, the limitations and harms associated with them have become more apparent. As a result, experts are now encouraging patients to discuss with their doctors the pros and cons of any cancer screening they are considering, and not just assume that testing is wholly beneficial.
“First, what people need to understand is that recommended screening tests are good, but they’re not perfect,” says epidemiologist Robert A. Smith, the director of cancer screening at the American Cancer Society. For starters, doctors often need to screen thousands of people to save just one life.
And because screening tests are not perfect, even the best test will miss some cancers. This means that some people will be told their test results were normal when they really do have cancer (this is called a false-negative result). Others will have a false-positive result, which will lead them to think they have cancer when they don’t. These false positives can result in significant—yet ultimately unnecessary—additional testing and anxiety.
Another critical but less understood problem is overdiagnosis. This happens when a screening test picks up a cellular abnormality that will never actually become dangerous. “There are things that look like cancer under the microscope, but they don’t behave like cancer,” explains internist Lisa Schwartz, a co-director of the VA Outcomes Group at the Veterans Affairs Medical Center in White River Junction, Vt., which focuses its work, in part, on the benefits and harms related to cancer screening.
Some of these abnormalities are harmless because they grow so slowly that they never cause any symptoms. Others may grow into a cancer that remains dormant—or even regresses—throughout a person’s lifetime. Currently, though, there is no way to know which aberrations picked up by screening will turn out to be dangerous and which won’t, so doctors typically treat them all.
As Schwartz explains, “If that cancer was never destined to progress, then any treatment for that cancer can only cause harm, because there was nothing to fix.”