A Tree-based Bayesian Accelerated Failure Time Cure Model for Estimating Heterogeneous Treatment Effect

Estimating heterogeneous treatment effects has drawn increasing attention in medical studies, considering that patients with divergent features can undergo a different progression of disease even with identical treatment. Such heterogeneity can co-occur with a cured fraction for biomedical studies with a time-to-event outcome and further complicates the quantification of treatment effects. This study considers a joint framework of Bayesian causal forest and accelerated failure time cure model to capture the cured proportion and treatment effect heterogeneity through three separate Bayesian additive regression trees. Under the potential outcomes framework, conditional and sample average treatment effects within the uncured subgroup are derived on the scale of log survival time subject to right-censoring, and treatment effects on the scale of survival probability are derived for each individual. Bayesian backfitting Markov chain Monte Carlo algorithm with the Gibbs sampler is conducted to estimate the causal effects. Simulation studies show the satisfactory performance of the proposed method. The proposed model is then applied to a breast cancer dataset extracted from the SEER database to demonstrate its usage in detecting heterogeneous treatment effects and cured subgroups. Combined with popular mitigation strategies, the proposed method can also alleviate confounding induced by immortal time bias.