Cancer, concepts, cohorts and complexity: avoiding oversimplification of overdiagnosis
Cancer, concepts, cohorts and complexity: avoiding oversimplification of overdiagnosis
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DOI：
10.1136/thoraxjnl-2012-201779
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发表时间：
2012-09-01
期刊：
影响因子：
10
通讯作者：
Detterbeck, Frank C.
中科院分区：
文献类型：
--
作者：
Detterbeck, Frank C.
OVERVIEW OF OVERDIAGNOSIS Extensive evidence indicates that overdiagnosis occurs in many cancers3; although difficult to quantify, the proportion is substantial. Autopsy studies, and studies involving resections for nonmalignant reasons (eg, prostatic hypertrophy), suggest undiagnosed prostate, thyroid, breast or lung cancers exist in 10e70% of middle-aged and older individuals. 3e5 In addition, long-term followup of randomised screening studies (allowing for ‘catch-up’cancers that are diagnosed later in the non-screened arms), suggests that 15e50% of breast and lung cancers represent overdiagnosis in mammography and chest radiograph screening studies. 3 6 7 Probably the strongest evidence comes from population-based studies demonstrating that in many cancers the rate of diagnosis has doubled or tripled, yet the death rate remains unchanged (eg, melanoma, thyroid, renal carcinoma). 3 The increased rate of diagnosis typically tracks consistently with increased use of methods of detection (ie, skin biopsies or imaging). 3 This phenomenon is not only restricted to cancer; while the death rate from pulmonary embolism has been stable, the incidence has increased dramatically since 2000, neatly tracking the rate of use of CT angiography for diagnosis. 8 However, overdiagnosis is not an inevitable consequence of screening as there is little evidence of overdiagnosis resulting from screening for cervical and colon cancer. 3 The traditional view is that any cancer that is not fatal (if left untreated) is an overdiagnosed cancer (figure 1). 9 Thus, an indolent tumour that does not grow significantly, does not cause symptoms, and allows the patient to die of other causes at a ripe old age is an overdiagnosed cancer. The idea of classifying such tumours as overdiagnosed is readily accepted, although there may be hesitation among clinicians who, traditionally, have only encountered life-threatening cancers to accept the premise that such indolent and inconsequential cancers exist.However, problems arise when one considers that overdiagnosis also includes other situations. Tumours grow at varying rates; a tumour would be labelled as overdiagnosed if a decision was made not to treat a slow-growing tumour in a vigorous 70-year-old man who eventually dies of the cancer at the age of 80 years (figure 2). At the other extreme, even an extremely rapidly growing cancer is ‘overdiagnosed’if the patient dies of some other cause (figure 2), which may be an unexpected event (eg, being struck by a bus), or an expected one from a major co-morbidity (eg, congestive heart failure). Each of these situations have very different implications for the individuals involved, our ability to predict their risk, and how we approach them in clinical patient management. The crux of the problem is that the concept of overdiagnosis hangs on the cause of death, or actually more precisely the time of death. A patient diagnosed with cancer who dies at the point he/she is ‘destined’to die has an overdiagnosed cancer; a patient who would have died of cancer but whose death is delayed because the cancer was diagnosed and treated is not overdiagnosed. Thus, implicit in the concept is the notion of time when a patient is destined to die, and that this can be altered for those destined to die of cancer. The concept assumes that treatment at preventing or delaying death from cancer is effective; by definition, a patient is classified as overdiagnosed if the treatment is ineffective, or if a decision is made not to treat, even though the patient dies of the cancer. A cancer is considered overdiagnosed even if treatment effectively palliates the symptoms but does not delay death.
