Overdiagnosis in lung cancer screening

There have been hundreds of publications about overdiagnosis during the past decade describing concern regarding its potential for harms in lung cancer screening. However, the definition and frequency with which it occurs in screening trials remains unclear. This lack of clarity stems from its current definition which is not based on a clinical grounds but instead on an epidemiologic definition that depends on the cause of death. Thus, with the current definition an overdiagnosed cancer can only be diagnosed if the person does not die from the cancer, regardless of whether or not the cancer is aggressive or the treatment successful. Using a definition based on epidemiology rather than the clinical presentation is highly unusual. Furthermore, the frequency of overdiagnosis has also been a cause of great confusion. Prior to the results from the National Lung Screening trial (NLST), concerns were expressed that virtually all CT screen detected cancers would be overdiagnosed, yet the extended follow-up study of the National Lung Screening Trial shows that in essence there were virtually no overdiagnosis. Even more confusing is that it was previously suspected that there was a high rate of overdiagnosis when using chest radiographic screening and therefore as CT is a more sensitive imaging test and finds cancers even earlier, it would be presumed that the overdiagnosis rate for CT would be even be higher. A proposed change in the definition would focus more on the clinical manifestation of the cancer as to its aggressiveness as this can be diagnosed while the patient is alive. Using a definition that is based on clinical features, a cancer that manifests as a nonsolid nodule would be considered overdiagnosed if instead of being recognized as relatively indolent was instead thought to be an aggressive cancer. The concept of overtreatment arises if this nonaggressive cancer were treated aggressively.