arXiv subjects

Meinhard Kieser

Publications and source records attributed to Meinhard Kieser.

7 recordsLinked to original sources

arXiv2026

How to optimize dynamic borrowing in basket trials - A utility-based framework and results of a comparison study

Basket trials are clinical trials in which one treatment is investigated in multiple subpopulations within a single trial. The subpopulations are called strata in the following. Stratified cohorts are typical but not limited to early oncological trials, where targeted therapies can be investigated in different strata defined by tumor tissue. In terms of statistical methodology, the stratification of the trial can be leveraged using information borrowing. The idea is that the strata will be analyzed separately if they respond differently to treatment, but that a stratum may share information from another if their response rates are similar. This can increase power while keeping type-I error inflation moderate. The borrowing methods can be tuned with respect to possible outcome scenarios. In this paper, we provide a framework for tuning basket trials: The compromise between power and type-I error rate is defined by a utility function which is then optimized using optimization algorithms. We investigated this framework by performing a pre-specified comparison study. Part I of the study compared optimization algorithms in terms of reliability and efficiency, part II compared the statistical performance of utility functions in simulated scenarios. This study shows how targeting different utility functions based on measures such as local power in each stratum or the number of correct decisions leads to different borrowing behavior of the optimized design. Furthermore, we discuss a mathematical counterexample which shows that no uniformly most powerful (UMP) test exists for basket trials, thus showing the limitations of basket trials. While information borrowing may result in power gains for some scenarios, there is no design which is optimal for all possible scenarios. Hence, a transparent optimization procedure is crucial when planning basket trials.

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arXiv2024

Utility-based optimization of Fujikawa's basket trial design -- Pre-specified protocol of a comparison study

Basket trial designs are a type of master protocol in which the same therapy is tested in several strata of the patient cohort. Many basket trial designs implement borrowing mechanisms. These allow sharing information between similar strata with the goal of increasing power in responsive strata while at the same time constraining type-I error inflation to a bearable threshold. These borrowing mechanisms can be tuned using numerical tuning parameters. The optimal choice of these tuning parameters is subject to research. In a comparison study using simulations and numerical calculations, we are planning to investigate the use of utility functions for quantifying the compromise between power and type-I error inflation and the use of numerical optimization algorithms for optimizing these functions. The present document is the protocol of this comparison study, defining each step of the study in accordance with the ADEMP scheme for pre-specification of simulation studies.

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arXiv2024

A basket trial design based on power priors

In basket trials a treatment is investigated in several subgroups. They are primarily used in oncology in early clinical phases as single-arm trials with a binary endpoint. For their analysis primarily Bayesian methods have been suggested, as they allow partial sharing of information based on the observed similarity between subgroups. Fujikawa et al. (2020) suggested an approach using empirical Bayes methods that allows flexible sharing based on easily interpretable weights derived from the Jensen-Shannon divergence between the subgroup-wise posterior distributions. We show that this design is closely related to the method of power priors and investigate several modifications of Fujikawa's design using methods from the power prior literature. While in Fujikawa's design, the amount of information that is shared between two baskets is only determined by their pairwise similarity, we also discuss extensions where the outcomes of all baskets are considered in the computation of the sharing weights. The results of our comparison study show that the power prior design has comparable performance to fully Bayesian designs in a range of different scenarios. At the same time, the power prior design is computationally cheap and even allows analytical computation of operating characteristics in some settings.

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arXiv2022

Analysis and sample size calculation within the responder stratified exponential survival model

The primary endpoint in oncology is usually overall survival, where differences between therapies may only be observable after many years. To avoid withholding of a promising therapy, preliminary approval based on a surrogate endpoint is possible. The approval can be confirmed later by assessing overall survival within the same study. In these trials, the correlation between surrogate endpoint and overall survival has to be taken into account for sample size calculation and analysis. For a binary surrogate endpoint, this relation can be modeled by means of the responder stratified exponential survival (RSES) model proposed by Xia, Cui, and Yang (2014). We derive properties of the model and confidence intervals based on Maximum Likelihood estimators. Furthermore, we present an approximate and an exact test for survival difference. Type I error rate, power, and required sample size for both newly developed tests are determined exactly. These characteristics are compared to those of the logrank test. We show that the exact test performs best. The power of the logrank test is considerably lower in some situations. We conclude that the logrank test should not be used within the RSES model. The proposed method for sample size calculation works well. The interpretability of our proposed methods is discussed.

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arXiv2020

Enhancing single-arm phase II trials by inclusion of matched control patients

When a novel treatment has successfully passed phase I, different options to design subsequent phase II trials are available. One approach is a single-arm trial, comparing the response rate in the intervention group against a fixed proportion. Another alternative is to conduct a randomized phase II trial, comparing the new treatment with placebo or the current standard. A significant problem arises in both approaches when the investigated patient population is very heterogeneous regarding prognostic factors. For the situation that a substantial dataset of historical controls exists, we propose an approach to enhance the classic single-arm trial design by including matched control patients. The outcome of the observed study population can be adjusted based on the matched controls with a comparable distribution of known confounders. We propose an adaptive two-stage design with the options of early stopping for futility and recalculation of the sample size taking the matching rate, number of matching partners, and observed treatment effect into account. The performance of the proposed design in terms of type I error rate, power, and expected sample size is investigated via simulation studies based on a hypothetical phase II trial investigating a novel therapy for patients with acute myeloid leukemia.

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arXiv2018

Sample size calculation and blinded recalculation for analysis of covariance models with multiple random covariates

When testing for superiority in a parallel-group setting with a continuous outcome, adjusting for covariates (e.g., baseline measurements) is usually recommended, in order to reduce bias and increase power. For this purpose, the analysis of covariance (ANCOVA) is frequently used, and recently, several exact and approximate sample size calculation procedures have been proposed. However, in case of multiple covariates, the planning might pose some practical challenges and surprising pitfalls, which have not been recognized so far. Moreover, since a considerable number of parameters have to be specified in advance, the risk of making erroneous initial assumptions, leading to substantially over- or underpowered studies, is increased. Therefore, we propose a method, which allows for re-estimating the sample size at a prespecified time point during the course of the trial. Extensive simulations for a broad range of settings, including unbalanced designs, confirm that the proposed method provides reliable results in many practically relevant situations. An advantage of the reassessment procedure is that it does not require unblinding of the data. In order to facilitate the application of the proposed method, we provide some R code and discuss a real-life data example.

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arXiv2016

Optimal adaptive two-stage designs for single-arm trial with binary endpoint

Minimizing the number of patients exposed to potentially harmful drugs in early onco logical trials is a major concern during planning. Adaptive designs account for the inherent uncertainty about the true effect size by determining the final sample size within an ongoing trial after an interim look at the data. We formulate the problem of finding adaptive designs which minimize expected sample size under the null hypothesis for single-arm trials with binary outcome as an integer linear program. This representation can be used to identify optimal adaptive designs which improve previous designs in two ways: Firstly, designs can be found exhibiting lower expected sample size under the null hypothesis than those provided by previous algorithms. Secondly, we explain how integer programming techniques can be exploited to remove pathologies of the optimal and previous solutions arising from the discrete nature of the underlying statistics. The resulting designs are both efficient in terms of expected sample size under the null hypothesis and well interpretable.

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