Pancreatic cancer patient‐derived organoids form stroma‐containing tumors on porcine urinary bladder. A) Schematic representation depicting the procedure for isolation, propagation, and engraftment of patient‐derived organoid (PDO) on porcine urinary bladder (PUB). B) Hematoxylin and eosin (H&E) stained histological sections of PDOs propagated on PUB for five days (n = 6). Arrows indicate tumor glands. C) Immunohistochemistry stainings for CDH1, CK‐19, VIM, KI‐67, and GATA6 of PDOs propagated on PUB for five days (n = 6). D) qRT‐PCR analysis (principal component analysis and heatmap of normalized RNA expression levels) of a relevant 14‐gene classical/basal‐like panel in PDOs propagated either on PUB or as 3D in vitro cultures (OR). E) Schematic representation illustrating the generation of assembloids consisting of PDOs and pancreatic stellate cells (PaSteCs) on PUB. F) H&E stained histological sections and immunofluorescence stainings for CK‐19 (red) and VIM (green) of PDO‐PaSteC assembloids cultured on PUB (n = 7). Cells were counterstained with DAPI (blue). Arrows indicate tumor glands/cancer cells. G) Schematic illustration depicting the generation of PDO, PaSteC, and peripheral blood mononuclear cells (PBMCs)‐containing assembloids on PUB. H) H&E stained histological sections and immunofluorescence stainings for CK‐19 (red) and VIM (green; left panel) or CD3E (green, right panel) of PDO‐PaSteC assembloids propagated on PUB for five days (n = 4). Immunofluorescence stainings for I) CD3E (green) and CD8A (red), and for J) KI‐67 (green on left panel; red on middle and right panels) and CK‐19 (red, left panel), VIM (green, middle panel), or CD3E (green, right panel) of PDO‐PaSteC‐PBMC assembloids propagated on PUB for five days (n = 4). K) Immunohistochemistry stainings for CDH1, CK‐19, VIM, KI‐67, and GATA6 of a pancreatic ductal adenocarcinoma patient liver metastasis biopsy. Scale bars represent 100 µm. PDAC, pancreatic ductal adenocarcinoma.