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05 June 2018

Overall Survival and Progression Free Survival extrapolation is important for HTA submissions for cancer treatments to UK NICE and other cost utility analysis country HTAs. Clinical opinion, historical trials and Real World Evidence are used to evaluate the fit of the distributions and to select the distributions most in line herewith. In previous work presented at ISPOR Europe 2017, we showed that different distributions can fit the Kaplan Meier equivalently well, resulting in about the same estimated average survival for the trial period, while the extrapolated part was different depending on which distribution we chose. As such, it is important to consider the extrapolation part in detail when needing it for HTA submissions.

Objective:

Methodology is developed to incorporate clinical opinion in the estimation process using prior distributions, rather than only using it to assess face validity.

Results:

Using prior distributions for the survival probability at certain time points, the parameters of standard distributions like exponential, Weibull, Gompertz, Generalized Gamma, lognormal, loglogistic and extensions with spline and cure models were estimated for Keynote 24. Different assumptions were formulated into prior distributions related to the hazard ratio at 5 years and 10 years, given that the ratio between hazards stayed the same, that it declined, and that there was no treatment effect remaining.

Conclusion:

By using prior distributions, it is possible to take clinical opinion around long-term survival into account in the estimation process leading to more reasonable extrapolations.

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