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To the EditorStedman’s Medical Dictionary defines the word indolent as follows: “inactive; sluggish; painless or nearly so, said of a morbid process.”1 In the arena of cancer screening, indolent disease refers to disease that need not be detected (or treated) because it is not and never will be life-threatening. The identification of indolent disease is most definitely a harm of cancer screening, and indolent disease is one component of overdiagnosed disease. Overdiagnosis also occurs when screening detects nonindolent disease that never would have been diagnosed in the absence of screening; that occurs because death due to other causes occurs prior to what would have been the date of symptomatic diagnosis in the absence of screening. We can refer to that as overdiagnosis due to competing causes of mortality. In the abstract of their important article quantifying overdiagnosis in lung cancer screening with low–radiation dose computed tomography, Patz et al2 incorrectly equate overdiagnosed cancers with indolent cancers. It is fair to assume that some portion of overdiagnosed lung cancers are indolent, but it must also be recognized that competing causes of mortality contribute to overdiagnosis. This is of particular importance in lung cancer screening because those most likely to be screened often have other life-threatening conditions, such as cardiovascular disease or chronic obstructive pulmonary disorder.
Marcus PM. Estimating Overdiagnosis in Lung Cancer Screening. JAMA Intern Med. 2014;174(7):1198. doi:10.1001/jamainternmed.2014.1546