**3. Patient-derived organoid and tumoroid**

The current paradigm for preclinical cancer drug development entails extensive and expensive optimization for lead discovery, often using *in vitro* human-cancercell-based models or *in vivo* animal-based tumor models that do not closely mirror actual solid tumors and, therefore, with little translational value [16]. Multicellular cancer "oids," including tumoroids, spheroids, and organoids, can address the existing loopholes in conventional 2D human cancer cell cultures and *in vivo* animal-based cancer models. Cancer "oids" display physiologically relevant cell-cell and cell-matrix interactions, gene expression and signaling pathway profiles, heterogeneity, and structural complexity, all of which are the characteristics of *in vivo* malignancies [17]. When cultivated appropriately, tumoroids develop easily and exhibit the *in vitro* model system's efficacy, repeatability, and resilience. Preclinical researchers are using tumoroids to present case studies on basic tumor biology, host-tumor interactions, and the application of high-throughput screening platforms for anticancer drug discovery and development [18]. This section discusses the evolution of organoids and research trends in cancer research.

This section also reviews patient-derived organoids (PDOs) as a revolutionary model system for cancer research. To circumvent the limitations of established cell lines, PDOs have recently been produced from varied tumor types [18, 19]. Researchers standardized 3D organoid culture methods to expand epithelial stem cells further and differentiate them into genetically and phenotypically stable "miniorgans in a dish," not only for humans but also for other species [17]. The *in vitro* response of PDOs mimics that of the result of related patients [20]. PDOs might be used to test immunomodulatory drugs in co-culture with different immune cell types. This book also addresses significant organoid-based bench-to-bedside applications and provides an overview of the therapeutic areas where organoids transform drug discovery and development.
