a, All metastases arising from adeno-Cre-transduced MMTV-PyMT; Cdh1+/+ organoids are E-cad+. Only mG+ metastases arising from adeno-Cre-transduced MMTV-PyMT; Cdh1fl/fl organoids are E-cad−. b, Number of macrometastases in mice transplanted with adeno-Cre-transduced MMTV-PyMT; Cdh1+/+ or Cdh1fl/fl tumour organoids, as sorted by the colour of the metastasis (mT, mG or mT/mG mixed). Horizontal line shows the median. ****P < 0.0001 (Kruskal–Wallis test). c, Number of macrometastases per mouse after tail-vein injections of adeno-Cre-transduced MMTV-PyMT; Cdh1+/+ or Cdh1fl/fl clusters, as sorted by the colour of the metastasis (mT, mG or mT/mG mixed) is represented. Horizontal line shows the median. ****P < 0.0001 (two-way ANOVA). d, Schematic of 3D-invasion assays using organoids from the same MMTV-PyMT; Cdh1fl/fl tumour with or without adeno-Cre transduction. e, Representative DIC images of MMTV-PyMT; Cdh1fl/fl organoids with or without adeno-Cre. Arrowheads, dissemination events. Scale bar, 50 μm. f, g, There is an increase in invasion (f) and dissemination (g) in Cdh1fl/fl organoids treated with adeno-Cre, relative to uninfected controls. Box plots show the median, box edges represent the first and third quartiles, and the whiskers extend to 5th and 95th percentiles. ****P < 0.0001 (Mann–Whitney test, two-sided). h, i, Schematic of the transplant assay using MMTV-PyMT; Cdh1fl/fl organoids with or without adeno-Cre (h). There are no observable E-cad− macrometastases (i). Horizontal line shows the median. **P = 0.0022 (Mann–Whitney test, two-sided). j, k, Schematic of the tail-vein assay using MMTV-PyMT; Cdh1fl/fl organoids with or without adeno-Cre (j). E-cad- cancer cells are defective at tumour-cell seeding (k). Horizontal line shows the median. **P = 0.0087 (Mann–Whitney test, two-sided). l, Schematic of orthotopic transplantation of adeno-Cre-transduced MMTV-PyMT; Cdh1+/+ or MMTV-PyMT; Cdh1fl/fl tumour organoids into immunocompetent FVB host mice. Lungs from these mice were collected after ~8 weeks and the number of metastases was counted. m, Number of observed macrometastases in FVB mice transplanted with adeno-Cre-transduced MMTV-PyMT; Cdh1+/+ or Cdh1fl/fl tumour organoids, sorted by the colour of the metastasis. Horizontal line shows the median. **P = 0.0033, *P = 0.024 (two-way ANOVA). n, Left, all metastases arising in control mice are E-cad+. Only mG+ cells containing metastases in adeno-Cre-transduced MMTV-PyMT; Cdh1fl/fl host mice are E-cad−. Right, E-cad− cancer cells do not contribute to observable macrometastases in adeno-Cre-transduced MMTV-PyMT; Cdh1fl/fl immunocompetent host mice. Horizontal line shows the median. ****P < 0.0001 (Mann–Whitney test, two-sided). Source data