To verify the epithelial or mesenchymal nature of the input primary tumor cells, we embedded organoids in agarose and subjected them to formalin-fixed, paraffin-embedded (FFPE) tissue processing and immunofluorescence (IF) to detect epithelial cytokeratin (using pan-cytokeratin antibody clone AE1/AE3) and the mesenchymal marker vimentin.28 Here, VIM is linked to neoplasm.