The extracellular matrix (ECM) is a complex network of macromolecules that provides physical structure support for tissues and acts as a reservoir for multiple growth factors and signaling mediators modulating the behavior of both cancer and stromal cells within the tumor microenvironment (TME). This key element of the tumor milieu significantly influences various cancer features such as cell differentiation, proliferation, angiogenesis, immune escape, invasion, and metastasis. Therefore, to accurately mimic tumors, it is essential that in vitro models include ECM components. Therefore, to develop 3D biomimetic models for studying cancer, researchers have explored various approaches, including scaffolds made from natural or synthetic polymers and ceramics. However, decellularized ECM derived from patient tumors presents a distinctive model since it preserves the native ECM architecture, biomechanical properties, and molecular composition. Here, we spotlight innovative and advanced protocols to obtain 3D models based on patient-derived decellularized ECM as high-throughput strategies for cancer research, particularly to immunotherapy screening.