One of my favorite topics to blog about for SBM is the topic of overdiagnosis and overtreatment. These are two interrelated phenomena that most people are blissfully unaware of. Unfortunately, I’d also say that the majority of physicians are only marginally more aware than the public about these confounders of screening programs, if even that.
Overdiagnosis has long been appreciated to be a major impediment to translating programs to screen for disease into better outcomes in a number of diseases but has only recently really seeped into the public consciousness, beginning in particular in 2009 when the United States Preventative Services Task Force (USPSTF) issued mammography recommendations that pushed back the recommended age to start screening to 50. Certainly, the concept of overdiagnosis is counterintuitive. After all, why do we screen for disease in asymptomatic people? The reason is simple—and maddeningly intuitive. We screen for disease based on the belief that catching potentially deadly diseases like cancer early, before they produce clinical symptoms, will allow earlier intervention and save lives. It seems blindingly obvious that this should be the case, doesn’t it? Unfortunately, real life biology and pathophysiology aren’t quite so neat and tidy, and the relationship between early detection and improved survival is muddied by phenomena such as lead time bias and the Will Rogers effect, in addition to overdiagnosis.
What is overdiagnosis? In brief, it is the detection of pathology or disease that, if left untreated, would never endanger the life of a patient or even harm him. Note that overdiagnosis is not the same thing as a false positive. A false positive occurs when a test detects disease that isn’t really there; in contrast with overdiagnosis there is definite pathology. The disease being screened for is there, at least in an early form. It’s just that, at the very early stage detected, it’s either not progressive or so indolent that the patient will grow old and die of something else before it would ever cause a problem. Indeed, it’s been estimated that as many as one in three breast cancers detected by mammography in asymptomatic women might be overdiagnosed and that one in five might spontaneously regress. However, because we don’t know which ones are unlikely to cause harm and haven’t worked out a safe method of observing them and intervening if they look as though they are progressing, we are obligated to treat them all when discovered. The problem of overdiagnosis has led to multiple alterations in what once were considered definitive recommendations for screening mammography, first by the USPSTF and most recently by the American Cancer Society.