Estimation of Lag Time Between Onset of and Death from an Occult Tumor

Abstract

A new statistical method for estimating the lag time between onset of and death from an occult tumor is proposed for data without cause-of-death information. In this method, the survival function for time to tumor onset, tumor-specific survival function, and competing risks survival function are estimated using the maximum likelihood estimates of the parameters. The proposed method utilizes the estimated survival functions and statistically imputed fatal tumors to estimate the lag time. This approach is developed for rodent tumorigenicity assays that have at least one interim sacrifice and a terminal sacrifice. If the data contains cause-of-death information given by pathologists and it is believed to be reliable, it may be used for estimating the lag time. The proposed method is illustrated using a real data set. The accuracy of the estimation of lag time is evaluated via a Monte Carlo simulation study. Our study shows that the estimated lag time is quite reliable.

Statistical evaluation of toxicological bioassays – a review

“…skin tumors). Because direct observation of the tumor onset times is not possible for types (i) and (ii), 116 the evaluation is possible only under some strong assumptions. Consequently, no optimal approach for a particular bioassay exists.…”