As indicated by cytokeratin-19 (K19) immunofluorescence and hematoxylin & eosin staining of single cell-derived branching organoids and corresponding orthotopic tumors, the system indeed displays prominent features of tumor morphogenesis in vivo, including the formation of tubular structures (Fig. 1f, Fig. S1b, c). This evidence concerns the gene KRT19 and neoplasm.