Robust transfer learning for accelerated failure time model

Limited sample sizes can impair the statistical accuracy of traditional survival models, resulting in potentially unsatisfactory conclusions. To address this issue, we propose a robust transfer learning framework for the accelerated failure time model (RTrans-AFT) that enables efficient and flexible information borrowing from an external source. The method accommodates both individual-level and summary-level source data and models differences in regression coefficients between cohorts without requiring identical covariate distributions. To control the degree of transfer, we impose an adaptive lasso penalty to control the discrepancy between the source and target parameters. This allows the method to selectively borrow information from the source cohort in the presence of heterogeneity, while fully incorporating external information when the two cohorts are comparable. Importantly, the framework is robust to potential data irregularities, such as outliers, which are common in real-world survival datasets. We establish the consistency and asymptotic normality of the proposed estimator. Simulation studies demonstrate that RTrans-AFT substantially improves estimation accuracy and achieves notable variance reduction, leading to enhanced statistical efficiency. The practical utility of the method is further illustrated through an analysis of lung adenocarcinoma data, where the Surveillance, Epidemiology, and End Results (SEER) registry data serve as the external source.