3D fibrin and type I collagen for 5 d. Quantitative results are expressed as the number of invasive foci per microscopic field (n = 3). (C) Light micrographs of fibrin and collagen cross-sections visualize the invasion of Bowes cells transfected with the indicated siRNAs. White dotted lines mark the surface of the matrix. (D) Cells transfected with the indicated siRNAs were embedded in 3D collagen type I gels as single cell suspension. Light micrographs show the cells after 5-d assay (n = 3). (TIF) Acknowledgments We thank Anne Remes and Sami Starast for excellent technical assistance and Biomedicum Helsinki Molecular Imaging Unit for imaging facilities. References 1. Nguyen DX, Bos PD, Massague J (2009) Metastasis: From dissemination to organ-specific colonization. Nat Rev Cancer 9(4): 274–284. 2. Hanahan D, Weinberg RA (2011) Hallmarks of cancer: The next generation. Cell 144(5): 646–674. 3. 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