Application of in vitro and in vivo cancer models to study the impact of the tumor immune microenvironment on anticancer therapy.

The tumor microenvironment is a dynamic, heterogeneous cellular ecosystem that includes cancer cells, cancer-associated fibroblasts (CAFs), endothelial cells, and immune cells. Immortalized cancer cell lines specific to a particular cancer type have been extensively used to investigate the anticancer effects and functional aspects of novel drugs. However, cancer cell lines do not accurately mimic the complex multicellular nature of organs. Since species-specific differences in mouse models of human cancer impact the interpretation of therapeutic efficacy, efforts have been made to reduce and replace the use of animals in the drug development process. It is now acknowledged that existing tumor models may not adequately simulate the tumor microenvironment. This has led to an increasing need for complex tumor models that can accurately represent the tumor immune microenvironment (TIME). The Organ-on-Chip (OoC) device has features that enable high-throughput screening and repeatable drug testing procedures by accurately simulating the tumor microenvironment (TME). Furthermore, although animal models remain vital for systemic analysis, the interpretation of therapeutic efficacy is often hindered by species-specific differences in immune and physiological responses. This limitation has created a critical conceptual gap in preclinical research. We acknowledge the pressing need for complex tumor models that can accurately simulate the tumor immune microenvironment (TIME). The immune system plays two key roles in cancer: fighting tumors and promoting the development of carcinogenesis. Recent advances have been made in understanding how the immune system contributes to cancer progression and the development of immune cell treatments for improved prognosis. In vivo and in vitro models have been created to investigate therapy resistance and the function of the tumor immune microenvironment (TIME) in anticancer therapy. This review provides a critical and balanced evaluation of the various in vitro (organoids, organ-on-chip, bioprinting) and in vivo (PDX, Humanized Mice) models utilized to study the TIME. We move beyond descriptive summaries to offer a functional comparison of these platforms, specifically delineating their utility in overcoming the clinical challenges of therapy resistance mechanisms and translational immunotherapy evaluations. This comparative approach demonstrates how advanced models, such as organ-on-chip (OoC), which enable dynamic control of the microenvironment and integration of multiple organs, can complement and refine the drug development process.