3D Bioprinting of Tumor Models for Cancer Research.

The exact mechanistic understanding of cancer metastasis continues to be unknown, although it is a major cause of death worldwide. Along with the tumor mass, the tumor microenvironment also contributes to pathogenesis and treatment resistance. Tumors are characterized by a high degree of heterogeneity and complexity. However, the fabrication of suitable in vitro models of the microenvironment is difficult as two-dimensional (2D) models do not completely recapitulate the biochemical and biophysical signals of the tumor environment. Thus, three-dimensional (3D) tumor models are emerging as vital tools for the comprehensive understanding of the sophisticated disease. Among different 3D models such as spheroid cultures, biopolymer scaffolds, organ on chip, and ex vivo tissue slices, 3D bioprinting has a competitive advantage due to the ability to precisely control and define the desired structure and position of multiple types of cells in a high-throughput manner. In this Review, we discussed the 3D bioprinted tumor models that integrate their microenvironment with different cell types, substrates, and bioprinting modalities and their application in drug screening and therapy. Finally, we highlighted the comprehensive understanding of the cancer microenvironment by 3D printed tumor models that are more physiologically relevant than the other models and expounded the challenges that need to be addressed for the clinical translation.