endothelial markers CD31 and CD34 and lymphatic marker LYVE-1. CD31 and CD34 show a staining pattern corresponding to that of pre-dyed endothelial cells, while these show no staining for LYVE-1. B – 3-dimensional reconstructions of spheroids, showing pre-dyed green endothelial cells as well as red staining for the markers indicated (CD31, CD34 and LYVE-1). (TIFF) Figure S3 Minitumour spheroids cultured for 7 days show lumen formation. Minitumour spheroids cultured for 7 days were fixed with glutaraldehyde, embedded in araldite epoxy resin, sectioned and imaged using a Tecnai G2 transmission electron microscope. Four different representative images are presented showing lumen formation (asterisk). Black arrow indicates a dying cell inside a lumen, probably in the process of its formation. f – fibroblast. Scale bar corresponds to 2 mm in A, B, C and 500 nm in D. (TIFF) Figure S4 MT1-MMP gene silencing in MDA-MB-231 cells has no effect on endothelial cell sprout formation. 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