Bioethics Blogs

The Question Isn’t Whether We Are Overdiagnosing Cancer, But How Much

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.

The views, opinions and positions expressed by these authors and blogs are theirs and do not necessarily represent that of the Bioethics Research Library and Kennedy Institute of Ethics or Georgetown University.