Abstract： Objective:To establish a paired organoid culture system for primary pancreatic cancer lesions and liver metastatic lesions in mice, and to investigate their morphological and biological behaviors.Methods:C57BL/6 mice aged 6 to 8 weeks were selected. Pancreatic cancer PANC02 cells carrying luciferase were injected into the pancreatic tail. After monitoring the formation of liver metastases using an in vivo imaging system, mice were sacrificed, and paired primary pancreatic cancer lesions and liver metastatic lesions were extracted and cultured in an in vitro organoid culture system. The formation process of organoids was observed under an inverted phase-contrast microscope. Hematoxylin and eosin staining was used to examine the morphological structure of the organoids. The expression of epithelial cell marker CK19 and proliferation marker Ki67 in the organoids was detected by immunohistochemistry and immunofluorescence staining. The expression of invasion markers N-cadherin, E-cadherin, vimentin, snail, and MMP9 was assessed by Western blotting and immunohistochemistry. The drug sensitivity of organoids to gemcitabine was evaluated using the CellTiter-Glo ? 3D Cell Viability Assay, and the half-maximal inhibitory concentration (IC 50) of the organoids was calculated. Results:A spontaneous liver metastasis model of pancreatic cancer in mice was successfully established, along with a paired organoid culture system for primary pancreatic cancer lesions and liver metastatic lesions. The organoids grew in a spherical shape and could be passaged up to 10 generations in vitro. Both liver metastatic lesion organoids and primary pancreatic cancer lesion organoids exhibited lumen-like structures, expressed the epithelial cell marker CK19, and the proliferation marker Ki67, with a significantly higher positive ratio of Ki67 in the liver metastatic lesions compared to the primary pancreatic cancer lesions. The expression levels of invasion markers N-cadherin, vimentin, snail, and MMP9 were significantly higher in liver metastatic organoids than in primary pancreatic cancer organoids, whereas the expression level of E-cadherin was significantly lower in liver metastatic organoids. The IC 50 value of gemcitabine for liver metastatic organoids was 165.0 nM, higher than the 108.5 nM for primary pancreatic cancer organoids. Conclusions:A stable, passagable organoids of primary pancreatic cancer lesions and liver metastatic lesions in mice were successfully established.