Using Individualized Treatment Effects to Assess Treatment Effect Heterogeneity.

Assessing treatment effect heterogeneity (TEH) in clinical trials is crucial, as it provides insights into the variability of treatment responses among patients, influencing key decisions related to drug development. Furthermore, it can lead to personalized medicine by tailoring treatments to individual patient characteristics. This paper introduces novel methodologies for assessing treatment effects using the individualized treatment effect as a basis. To estimate this effect, we use a doubly robust (DR) learner to infer a pseudo-outcome that reflects the causal contrast. This pseudo-outcome is then used to perform three objectives: (1) a global test for heterogeneity, (2) ranking covariates based on their influence on effect modification, and (3) providing estimates of the individualized treatment effect. We compare the DR-learner with various alternatives and competing methods in a simulation study, and also use it to assess heterogeneity in a pooled analysis of five Phase III trials in psoriatic arthritis (PsA). By integrating these methods with the recently proposed Workflow to Assess Treatment Effect Heterogeneity in Drug Development for Clinical Trial Sponsors (WATCH) workflow, we provide a robust framework for analyzing TEH, offering insights that enable more informed decision-making in this challenging area.