Breast cancer cell spheroid, SEM

False-coloured scanning electron micrograph (SEM) of a 3-day old breast tumour spheroid (cluster of cells). The red regions show areas of cells dying through a mechanism known as programmed cell death or "apoptosis". The spheroid is a 3D system used to test the therapeutic activity of anti-cancer drugs and can reduce the need for research on animals. Different layers of cells within the spheroid will be proliferating at different rates and will have varying accessibility to drugs. Diameter of the spheroid is approximately 250 micrometres.