Medical experts now agree that as a result of aggressive screening programs, we have an epidemic of cancer overdiagnosis in the United States. With mammograms finding tiny cancers and PSA tests discovering unpalpable prostate cancers, we are now unearthing some cancers too early for our own good.
What do experts mean by “overdiagnosis,” you ask? First, overdiagnosis is not the same as a misdiagnosis. If a pathologist looks under a microscope and classifies a group of benign cells as being cancerous, that is a misdiagnosis. Such misdiagnoses are an important consequence of cancer screening, causing patients to experience unnecessary anxiety and to undergo unnecessary treatments. Because no pathologist is perfect, aggressive screening programs will, by definition, lead to increases in such misdiagnoses. But these misdiagnoses do not qualify as overdiagnoses, the way experts use the term.
Second, overdiagnosis is not the same as a false positive test result. When a mammogram reveals a suspicious shadow, or when a PSA test is elevated, physicians usually follow up with additional tests, often culminating in a biopsy of the suspected lesion. When that testing reveals that no cancer is present, the screening test (the mammogram or the PSA test) is said to have created a “false positive,” result. It sent out a false alarm. Once again, false alarms are an important side effect of cancer screening. And more aggressive screening programs (yearly mammograms rather than every other year, for example) will necessarily lead to an increase in false positive test results. By some estimates, women beginning annual mammograms at age 40 will face a 50% lifetime risk of a false positive test. In other words, this is a burden of screening that we need to keep in mind when deciding how aggressively to look for a cancer. But false positives are not the same thing as overdiagnoses.
So what does it mean to overdiagnose cancer?
According to cancer epidemiologist Ruth Etzioni: “Overdiagnosis occurs when screening detects a tumor that would not have presented clinically in the absence of screening.” For example, if a mammogram reveals a tiny breast cancer in a 103-year-old woman, a cancer that if left alone would not grow large enough to cause symptoms (much less death) for another decade, that mammogram would probably have overdiagnosed her cancer—if she had never had that mammogram, she would have lived the rest of her life (maybe to 104 or 107-years-old) blissfully unaware that a small breast cancer was growing inside her body.
The example of this hypothetical 103-year-old woman is obviously an extreme one, meant to illustrate what experts mean by overdiagnosis. But it makes one thing clear. Cancer overdiagnoses are cases of real and true cancer. In this hypothetical case, for example, the tumor in this woman’s breast really was malignant. The mammogram did not lead to a misdiagnosis or to a false alarm. Instead, the mammogram discovered a cancer that, while real, would not have ever influenced this woman’s life. In her case, in fact, the diagnosis of this cancer would only act to harm this woman, by causing anxiety and potentially by leading to harmful treatments. (To read the rest of this article, please visit Forbes.)