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Abstract:
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This is an extension of the original probability method to decide when to initiate cancer screening for an asymptomatic individual. The major improvement is that screening sensitivity is a function of sojourn time and time spent in the preclinical state. The probability of incidence from one’s current age to the first exam is a function of the three key parameters (sensitivity, time duration in the disease-free state and the sojourn time in the preclinical state); and it is monotone increasing as time increases, given a person’s current age. So there exists a unique solution of the first screening time by limiting this probability to a small value, such as 10%. That is, with 90% probability, one will not be a clinical incident case before the first exam. After this time/age is found, we can further estimate the lead time distribution and probability of over-diagnosis if one would be diagnosed with cancer at the first exam. Simulations were carried out under different scenarios; and the method was applied to the male and female heavy smoker cohorts in the National Lung Screening Trial using low-dose computerized tomography. The method is applicable to other kinds of screening.
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