Extrapolation of Survival Benefits in Patients with Transthyretin Amyloid Cardiomyopathy Receiving Tafamidis: Analysis of the Tafamidis in Transthyretin Cardiomyopathy Clinical Trial

INTRODUCTION: In the Tafamidis in Transthyretin Cardiomyopathy Clinical Trial (ATTR-ACT; ClinicalTrials.gov number NCT01994889), tafamidis reduced the risk of all-cause mortality in patients with transthyretin amyloid cardiomyopathy (ATTR-CM) by 30% versus placebo. Median overall survival was not achieved in either treatment arm (57.1 and 70.5% of patients in the placebo and tafamidis groups, respectively, survived at 30 months), limiting assessment of the potential survival benefits of treatment. METHODS: A survival extrapolation analysis was conducted following technical support guidelines from the National Institute for Health and Care Excellence. Multiple models (i.e., exponential, Weibull, gamma, log-logistic, log-normal, Gompertz, generalized gamma, and generalized F) were applied to systematically fit different candidate curves to existing patient-level data from the 30-month treatment period in ATTR-ACT. The relative goodness-of-fit for each candidate curve was then tested by Akaike’s and Bayesian information criteria to select a single model that was fitted to the placebo and pooled tafamidis treatment arms. RESULTS: A gamma distribution was selected as best fitting model and fitted to both treatment arms. The resulting estimated median overall survival was 35.16 months for placebo and 52.64 months for tafamidis (difference 17.48 months). CONCLUSIONS: This extrapolation of survival data from ATTR-ACT further supports the efficacy of tafamidis in patients with ATTR-CM. Owing to the limitations of this analysis, these survival estimates should be interpreted with caution; however, they are consistent with recently presented findings from a combined analysis of data from ATTR-ACT and interim data from an ongoing long-term extension study (median follow-up 36 months; ClinicalTrials.gov number NCT02791230). TRIAL REGISTRATION: ClinicalTrials.gov: NCT01994889. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s40119-020-00179-2) contains supplementary material, which is available to authorized users.