Qingxia Chen, PhD, Department of Biostatistics, Vanderbilt University

"Treatment Effect Estimate and Model Diagnostics with Two-way Time-Varying Treatment Switching: an application to a head and neck study"

Treatment switching frequently occurs in clinical trials due to ethical reasons. Intent-to-treat analysis without adjusting for switching yields biased and inefficient estimates of the treatment effects. In this paper, we propose a class of semiparametric semi-competing risks transition survival models to accommodate two-way  time-varying switching to post-study therapy. Theoretical properties of the proposed model are examined. An efficient expectation-maximization algorithm is  derived and implemented in existing software to obtain the maximum likelihood estimates along with model diagnostic tools. Simulation studies are conducted to demonstrate the validity of the model. The proposed method is further applied to data from a clinical trial with patients having recurrent or metastatic squamous-cell carcinoma of the head and neck.

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