MCF-7 cells were plated on low adhesion plates and left for 48h undisturbed until spheroids formed.

<p>hTERT-immortalised fibroblasts transduced with dsRED, were then added and cocultured for a further 48h. Cells were imaged using a dual purpose phase contrast and fluorescence microscope, which allowed visualisation of cell distribution, defined by the fibroblasts’ red fluorescence and the MCF-7 cells’ lack of fluorescence under phase contrast. Scale bar = 400μm.