Q: What is the best definition of the "critical point" in the spread of cancer?
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A: When a cancer becomes difficult to cure. Please see image 1/10 for the explanation.
Q: What type of cancer screening bias may result from a cancer that never reaches the "critical point", i.e., the point at which it becomes difficult to cure?
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A: Overdiagnosis. "Overdiagnosis" refers to the detection of cancers with screening that would never have harmed a patient. This may occur as the result of either cancer that doesn't progress to the critical point or a cancer that progresses so slowly that the patient dies of a competing cause of death such as a myocardial infarction.
Q: What type of cancer screening bias may result from a cancer that slowly reaches the "critical point", i.e., the point at which it becomes difficult to cure?
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A: Length time. Because we have numerous opportunities (screening intervals) to detect slowly growing cancers with screening, screen-detected cancers tend to be less aggressive than those that are detected clinically after symptoms occur. This tendency is known as length time bias.
Q: What is the most characteristic feature of cancers that may lead to "length time" bias?
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A: Slow spread. Because we have numerous opportunities (screening intervals) to detect slowly growing cancers with screening, screen-detected cancers tend to be less aggressive than those that are detected clinically after symptoms occur. This tendency is known as length time bias.
Q: What type of cancer screening bias(es) result(s) in overestimation of the benefits of screening?
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A: Overdiagnosis and length time. Some cancers don't progress and won't put the patient's life at risk. Finding these cancers with screening doesn't help patients, but we may mistakenly credit the screening and the subsequent treatment for a good outcome. Because we have numerous opportunities (screening intervals) to detect slowly growing cancers with screening, screen-detected cancers tend to be less aggressive than those that are detected clinically after symptoms occur. This tendency is known as length time bias. The combination of overdiagnosis and length time may result in an overestimation of the benefit of screening.
Q: What type of cancer screening bias may result from a cancer that reaches the "critical point" (the point at which the cancer becomes difficult to cure) before it can be detected by screening?
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A: Lead time. Lead time bias occurs if screening results in the detection of cancer after it becomes incurable but before it would have been detected clinically (i.e., after the development of symptoms). Since we measure survival starting with the timepoint when a cancer is detected, there is a spurious increase in survival time in these aggressive screen-detected cancers compared to patients with similar cancers detected clinically because the diagnosis has been pushed back in time because of the screening.
Q: What study randomized >50,000 subjects into low-dose CT and chest x-ray screening groups and found a 20% reduction in lung cancer mortality in subjects screened with low-dose CT compared to chest x-ray screening?
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A: National Lung Screening Trial (NLST)