All Times ET
Keywords: Scheduling, Lead time, Overdiagnosis, Sensitivity, Sojourn time, Transition probability
This is an extension of the original probability method to decide when to initiate a cancer screening exam for an asymptomatic individual. The major improvement is that screening sensitivity is a function of the 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 (screening sensitivity, time duration in the disease-free state, and the sojourn time in the preclinical state); and it is monotonically increasing as time increases, given a person's current age. So we can find a unique solution for the first screening time by limiting this probability to a small value, such as 10% or 20%. That is, with a 90% or 80% probability, one will not be a clinical incident case before the first exam. After this first screening 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 disease screening. And the predictive information can be used by physicians or individuals at risk to make informed decisions on when to initiate screening.