Overdiagnosis
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2008-05-14T15:20:09Z
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'''Overdiagnosis''' is the [[diagnosis]] of "disease" that will never cause [[symptom]]s or death during a [[patient]]'s lifetime. Overdiagnosis is the least familiar [[side-effect]] of [[Screening (medicine)|testing for early forms of disease]] – and, arguably, the most important. It is a problem because it turns people into patients unnecessarily and because it leads to [[treatment]]s that can only cause harm.
Overdiagnosis occurs when a disease is diagnosed correctly, but the diagnosis is irrelevant. A correct diagnosis may be irrelevant because treatment for the disease is not available, not needed, or not wanted.
Because most people who are diagnosed are also treated, it is difficult to assess whether overdiagnosis has occurred in an individual. Overdiagnosis in an individual cannot be determined during life. Overdiagnosis is only certain when an individual remains untreated, never develops symptoms of the disease and dies of something else.
Thus most of the inferences about overdiagnosis comes from the study of [[population]]s. Rapidly rising rates of testing and disease diagnosis in the setting of stable rates of the feared outcome of the disease (e.g. death) are highly suggestive of overdiagnosis. Most compelling, however, is evidence from a randomized trial of a screening test intended to detect pre-clinical disease. A persistent excess of detected disease in the tested group years after the trial is completed constitutes the best evidence that overdiagnosis has occurred.
Although overdiagnosis is potentially applicable to the diagnosis of any disease, its origin is in [[cancer screening]] – the systematic evaluation of asymptomatic patients to detect early forms of [[cancer]]<ref>Welch HG. Should I Be Tested for Cancer? Maybe Not and Here’s Why. University of California Press (2006 paperback, 2004 hardback)</ref>. The central harm of cancer screening is overdiagnosis – the detection of abnormalities that meet the pathologic definition of cancer (under the microscope) but will never progress to cause symptoms or death during a patient's lifetime.
==Overdiagnosis and the variability of cancer progression==
Cancer screening is the effort to detect cancer early, during its pre-clinical phase — the time period that begins with an abnormal cell and ends when the patient notices symptoms from the cancer. It has long been known that some people have cancers with short pre-clinical phases (fast growing, agresssive cancers), while others have cancers with long pre-clinical phases (slow growing cancers). And this heterogeneity has an unfortunate implication: namely, screening tends to disproportionately detect slow growing cancers (because they are accessible to be detected for a long period of time) and disproportionately miss the fast growing cancers (because they are only accessible to be detected for a short period of time) – the very cancers we would most like to catch. For more information, see [[Screening_(medicine)#Length_time_bias]].
This long-standing model has a hidden assumption: namely, that all cancers inevitably progress. But some pre-clinical cancers will not progress to cause problems for patients. And if screening (or testing for some other reason) detects these cancers, overdiagnosis has occurred.
The figure below depicts the heterogeneity of cancer progression using 4 arrows to represent 4 categories of cancer progression.
<br />
[[Image:overdiagnosis1.jpg|thumb|450px|center|Cancer screening is most useful in detecting slowly progressing cancers but can cause overdiagnosis if very slow or non-progressive cancers are detected.]]<br />
The arrow labeled "Fast" represents a fast growing cancer, one that quickly leads to symptoms and to death. These are the worst forms of cancer and unfortunately often appear in the interval between screening tests. The arrow labeled "Slow" represents a slow growing cancer, one that leads to symptoms and death but only after many years. These are the cancers for which screening has arguably the greatest beneficial impact.
The arrow labeled "Very Slow" represents a cancer that never causes problems because it is growing very slowly. If a cancer grows slowly enough, then patients will die of some other cause before the cancer gets big enough to produce symptoms. This is particularly likely with small cancers in the elderly – prostate cancer in older men serves as the most prominent clinical example.
The arrow labeled "Non-progressive" represents a cancer that never causes problems because it is not growing at all. In other words, there are cellular abnormalities that meet the pathologic definition of cancer but never grow to cause symptoms – alternatively, they may grow and then regress. Although the concept of non-progressive cancers may seem implausible, basic scientists have begun to uncover biologic mechanisms that halt the progression of cancer<ref>Mooi WJ, Peeper DS. Oncogene-induced cell senescence--halting on the road to cancer. N Engl J Med. 2006;355:1037-46</ref><ref>Folkman J, Kalluri R. Cancer without disease. Nature. 2004;427:787.</ref><ref>Serrano M. Cancer Regression by Senescence. New Engl J Med 2007 356:1996-97.</ref>. Some cancers outgrow their blood supply (and are starved), others are recognized by the host's immune system (and are successfully contained), and some are not that aggressive in the first place.
Overdiagnosis occurs when either "Non-progressive" cancers or "Very Slow" growing cancers (more precisely, at a slow enough pace that individuals die from something else before the cancer ever causes symptoms) are detected. These two forms of cancer are collectively referred to as pseudodisease - literally false disease. Since the word "disease" implies something that makes, or will make, a person feel sick (something that causes symptoms), pseudodisease is an appropriate word for describing these abnormalities. Thus, another definition of overdiagnosis is simply the detection of pseudodisease.
==Evidence for overdiagnosis in cancer==
The phenomenon of overdiagnosis is most widely understood in [[prostate cancer]]<ref>Etzioni R, Penson DF, Legler JM, et. al. Overdiagnosis due to prostate-specific antigen screening: lessons from U.S. prostate cancer incidence trends. J Natl Cancer Inst. 2002;94:981-90.</ref>. A dramatic increase in the number of new cases of prostate cancer was observed following the introduction of the PSA (prostate specific [[antigen]]) screening test. Because of the problem of overdiagnosis most organizations recommend against prostate cancer screening in men with limited life expectancy - generally defined as less than 10 years (see also [[prostate cancer screening]]).
Overdiagnosis has been identified in mammographic screening for breast cancer<ref>Zahl PH, Strand BH, Mæhlen J. Breast cancer incidence in Norway and Sweden during introduction of nation-wide screening: prospective cohort study. BMJ 2004; 328: 921-4.</ref><ref>Gotzsche P, Nielsen M. Screening for breast cancer with mammography. Cochrane Database of Systematic Reviews 2006.</ref>. Long-term follow-up of the Malmo randomized trial of mammography found a persistent excess of 115 breast cancers in the screened group 15 years after the trial was completed<ref>Zackrisson S, Andersson I, Janzon L, Manjer J, Garne JP. Rate of over-diagnosis of breast cancer 15 years after end of Malmö mammographic screening trial: follow-up study. BMJ 2006; 332: 689-692.</ref>, suggesting that one-quarter of mammographically detected breast cancers represent overdiagnosis<ref>Welch HG, Schwartz LM, Woloshin S. Ramifications of screening for breast cancer: 1 in 4 cancers detected by mammography are pseudocancers. BMJ. 2006;332:727.</ref>.
Overdiagnosis has also been identified in chest x-ray screening for lung cancer<ref>Black WC. Overdiagnosis: An underrecognized cause of confusion and harm in cancer screening. J Natl Cancer Inst. 2000 Aug 16;92(16):1280-2.</ref>. Long-term follow-up of the Mayo Clinic randomized trial of screening with chest x-rays and sputum cytology found a persistent excess of 46 lung cancer cases in the screened group 13 years after the trial was completed<ref>Marcus PM, Bergstralh EJ, Fagerstrom RM, Williams DE, Fontana R, Taylor WF, Prorok PC. Lung cancer mortality in the Mayo Lung Project: impact of extended follow-up. J Natl Cancer Inst. 2000;92:1308-16.</ref>, suggesting that 20-40% of lung cancers detected by conventional x-ray screening represent overdiagnosis. There is considerable evidence that the problem of overdiagnosis is much greater for lung cancer screening using spiral-CT scans<ref>Welch HG, Woloshin S, Schwartz LM, Gordis L, Gøtzsche PC, Harris R, Kramer BS, Ransohoff DF. Overstating the evidence for lung cancer screening: the International Early Lung Cancer Action Program (I-ELCAP) study. Arch Intern Med. 2007;167:2289-95.</ref>
Overdiagnosis has also been associated with early detection in a variety of other cancers, including neuroblastoma<ref>Schilling FH, Spix C, Berthold F, et. al. Neuroblastoma screening at one year of age. N Engl J Med 2002 346:1047-1053.</ref><ref>Yamamoto K, Hanada R, Kikuchi A, et al. Spontaneous regression of localized neuroblastoma detected by mass screening. J Clin Oncol 1998;16:1265-69.</ref>, melanoma<ref>Welch HG, Woloshin S, Schwartz LM. Skin biopsy rates and incidence of melanoma: population based ecological study. BMJ. 2005;331:481-4.</ref>, and thyroid cancer<ref>Davies L, Welch HG. The increasing incidence of thyroid cancer in the United States, 1973-2002. JAMA 2006;295;2164-7.</ref>. In fact, some degree of overdiagnosis in cancer early detection is probably the rule, not the exception.
==Harms of overdiagnosis==
The fundamental paradox of early cancer detection is that while some may be helped, others get a diagnosis they'd be better off without. Overdiagnosed patients cannot benefit from the detection and treatment of their "cancer", because the cancer was never destined to cause symptoms or death. They can only be harmed. There are three categories of harm associated with overdiagnosis:
#Physical effects of unnecessary diagnosis and treatment: All medical interventions have side-effects. This is particularly true of cancer treatments. Surgery, radiation and chemotherapy all pose varying morbidity and mortality risks.
#Psychological effects: there is a burden for an individual simply being labeled as "diseased" (e.g. the burden of being labeled a "cancer patient") and an associated increased sense of vulnerability.
#Economic burden: Not only the associated cost of treatment (from which the patient cannot benefit, because the disease posed no threat), but also - at least, in the current health care system in the United States - a potential increase in the cost of health insurance or even an inability to procure it (e.g. the diagnosis creates a pre-existing condition that affects health insurance).
While many identify false positive results as the major downside to cancer screening, there are data to suggest that - when patients are informed about overdiagnosis - they are much more concerned about overdiagnosis than false positive results<ref>Schwartz LM, Woloshin S, Sox HC, Fischhoff B, Welch HG. US women's attitudes to false positive mammography results and detection of ductal carcinoma in situ: cross sectional survey. BMJ. 2000;320:1635-40.</ref>.
==Distinction between overdiagnosis and false positive results==
Overdiagnosis is often confused with the term "[[false positive]]" test results, but they are two distinct concepts. A false positive test result refers to a test that suggests the presence of disease, but is ultimately proved to be in error (usually by a second, more precise test). Patients with false positive test results are told they don't have disease and are not treated; overdiagnosed patients are told they have disease and generally receive treatment.
{|class="wikitable" style="width:100%" border="1" cellpadding="2"
!width="150"|
!width="225"|Overdiagnosis
!width="225"|False Positive Results
|-valign="top"
|'''''Definition''''' ||Detection of a "disease" that will never cause symptoms or death during a patients lifetime||A "false alarm" – an initial test result that suggests the presence of disease, but it is later proved that no disease is present.
|-valign="top"
|'''''Patient experience''''' ||Told they have the disease||Told that the test was wrong and they do not have the disease
|-valign="top"
|'''''Physician action'''''||Generally, initiates treatment||Reassurance
|-valign="top"
|'''''Potential Harms'''''||
*Physical effects: Side effects and mortality risk from treatments that cannot help the patient (because they did not need help)<br />
*Psychological effects: labeled as "diseased" and increased sense of vulnerability.
*Economic burden: Treatment costs, may create pre-existing condition that interferes with health insurance.
||
*Physical effects: Discomfort and complications from invasive diagnostic tests.
*Psychological effects: Short term anxiety associated with near miss (e.g. "cancer scare").
*Economic burden: Cost of diagnostic testing
|}
==Overdiagnosis bias in survival statistics==
Overdiagnosis, by contributing disproportionately to ''early'' diagnosis of lethal conditions, has the effect of inflating survival statistics<ref>Black W, Welch H. Advances in diagnostic imaging and overestimations of disease prevalence and the benefits of therapy. N Engl J Med 1993;328:1237-43.</ref><ref>Welch H, Schwartz L, Woloshin S. Are increasing 5-year survival rates evidence of success against cancer? . JAMA 2000;283:1975-78.</ref>. The more overdiagnosis, the better survival appears and it seems like early diagnosis is doing good. More testing is encouraged, leading to more overdiagnosis.
Overdiagnosis always inflates survival statistics. Survival rates (e.g. 5-year survival, 10-year survival) are calculated as the proportion of patients that are alive after a fixed period (e.g. 5 or 10 years) following diagnosis. Overdiagnosis inflates both the numerator and denominator of the survival statistic. The figure below shows how overdiagnosis - the detection of pseudodisease - inflates the survival statistic even when the number of deaths is stable.<br />
[[Image:Overdianosissurvival.jpg|thumb|600px|center|Overdiagnosis can inflate survival rates without any actual health benefits.]]<br /><br />
Imagine that there is no pseudodisease detected in current practice and that among 1000 patients diagnosed, only 100 are alive 10 years later (i.e. the 10-year survival is 100 divided by 1000 or 10%). Now imagine that in addition to identifying these cancers, spiral CT scanning also identifies 4000 patients with pseudodisease - all of whom survive 10 years, since they have non-progressive cancer. The new 10-year survival will include these patients in both the numerator and denominator - leading to a 10-year survival of 4100 divided by 5000 or 82%. Note that even though survival has changed dramatically, the number of people who die has not changed – under either condition 900 patients have died. This example demonstrates how survival can be increased by overdiagnosis, even if no one avoids death.
==Overdiagnosis in Psycho/Social Spheres==
Since the mid-1970s, the in-patient population of institutional facilities for the mentally ill and the mentally retarded has been dropping precipitously. While there is no suggestion that the mentally retarded (individuals generally at or below a 70 IQ) has changed from at or around 3% of any given population, the number of persons diagnosed with mental illness has increased rather dramatically.
There are a number of possible explanations. The American Psychiatric Association formulated the first Diagnostic and Statistical Manual of Mental Disorders before 1967 and those first efforts were contained in 134 pages. Subsequent manuals are (the DSM V is now being written) over 800 pages in length. The vast majority of described mental disorders will have practitioners who claim to be proficient in the diagnosis and treatment any given entry. None of the entries are tied to specific medical or laboratory findings, but are instead, descriptors of physical and social behavior. In other words, more descriptions of deviancy define ever more persons as deviant. The current manual (IV) describes caffeine addiction and bruxism as mental illnesses. By the standards of earlier eras, the description of rather common human behavioral ailments as mental illneses could be described as overdiagnosis.
Advocates of mental health treatment now report that as many as one-fifth of the children whose parents have experienced a divorce may need mental health treatment. While the divorce rate was lower fifty years ago, suggesting that a fifth of these children, most of whom attend school regularly and participate in normal childhood activities without major impairment, could be described as overdiagnosis, as well.
There has been an explosive growth in the numbers and types of psycho-active medications, and they are now marketed directly to the public. There is little doubt that the suggestion of a medication or treatment for what, in an earlier era, would have been considered within the normal range of life problems, may be yet another example of over-diagnosis. Examples of medical treatments for "new" diagnosis such as pediatric bi-polar disorder, which did not exist ten years ago, and is non-existent in other western cultures, certainly raises the possibility of overdiagnosis.
==See also==
*[[Patient education]]
==References==
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[[Category:Medical terms]]
[[Category:Medical tests]]