In drug discovery programs, multicellular spheroids and tumoroids have emerged as powerful tools to bridge the gap between in vitro cell culture models and in vivo tissues. 3D tumor cultures are a promising tool for in vitro rebuilding the in vivo behaviour of cancer cells for the development and validation of anti-tumor therapies. Yet, in vitro models capable to realistically mimic the complex ecosystem of solid tumors is an unmet need. In solid cancer mutual interactions between the epithelial transformed cancer cells and their surrounding partners, (including stromal non-transformed cells; carcinoma-associated fibroblasts, endothelial cells, adipocytes, pericytes, innate and adaptive immune cells) embedded within a complex extracellular matrix (ECM), favour tumor development, metastatic spreading and resistance to chemotherapeutic treatments. Therefore, the development of 3D multicellular spheroids and tumoroids embedded in a collagen rich matrix in vitro would significantly improve the early phase of drug discovery in preclinical cancer research.