Cancer ecosystems comprise not only cancer cells but also various stromal cells, such as mesenchymal and vascular endothelial cells. Pancreatic cancer is stroma-rich cancer, and the abundant stroma is considered responsible for the resistance to treatment and for poor prognosis. Accordingly, it is important to understand and control pancreatic cancer cell-stromal cell interaction. To analyze the interaction and further accurately assess the susceptibility to pancreatic cancer drugs, a culture system capable of recapitulating pancreatic cancer ecosystem is essential. We previously established a method to generate multi-lineage functional organs using human iPS cells (Takebe T, Sekine K et al, Nature, 2013; Sekine K, Camp JG et al, Nature 2017). By applying the three-dimensional tissue reconstruction technique to pancreatic cancer research, we succeeded in reconstituting human pancreatic cancer tissue (pancreatic cancer organoid) and recapitulating abundant stroma from patient-derived primary cancer cells. Evaluation of susceptibility of pancreatic cancer organoids in vitro and in vivo revealed that sensitivity to gemcitabine, a therapeutic drug for pancreatic cancer, is greatly reduced compared to the cancer cell only. In summary, pancreatic cancer organoids are an effective tool for reproducing the treatment resistance of pancreatic cancer patients and useful for drug screening. Currently, we are working on detailed analysis of patient tissue and recapitulation of advanced tissue structure with the aim of further improving the accuracy as a patient-derived cancer model.