Quantification by flow cytometry of the proportion of Notch1+ cells within tumour epithelial cells (selected with the markers EpCAM+/Lin-, see gate strategies in Supplementary Fig. 1), indicated, in agreement with our immunofluorescence results, that Notch1-expressing epithelial cells represent a rare tumour cell population comprising 1,2% ± 0,3% of tumour cells (Fig. 1c). Here, EPCAM is linked to neoplasm.