Tumor Assembloids as Three-Dimensional Platforms for Modeling Drug Delivery Barriers: Construction Strategies, Applications, and Translational Challenges.

A major limitation of conventional two and three-dimensional preclinical in vitro cancer models is their inability to reproduce the drug-delivery barriers. Tumor assembloids, which integrate patient-derived cancer cells with stromal, endothelial, and immune components in three-dimensional architectures, provide a manipulable framework for simulating these multicellular impediments. This review specifically examines the application of tumor assembloids to investigate drug delivery constraints, including stromal exclusion, vascular transport, immune-mediated resistance, penetration gradients, and spatially heterogeneous drug exposure. We compared three major construction strategies, including self-assembly, 3D bioprinting, and microfluidic compartmentalization, and evaluated their respective strengths for drug assessment. We also discussed assembloids' current limitations, including reproducibility, incomplete physiological dynamics, insufficient spatial analytics, and the need for standardized benchmarking. Overall, tumor assembloids represent promising mechanistic platforms for studying tumor drug delivery barriers. However, broader clinical application will necessitate rigorous validation and harmonized assay standards.