Breast cancer. Coloured transmission electron micrograph (TEM) of a section through a ductal carcinoma (cancer) of the breast showing malignant epithelial cells. An irregular nucleus, mitochondria and surface microvilli are all visible. This is a cancer that arises from the lining of the milk ducts and is the most common type of breast cancer. Human tissue. Magnification: x3000 when printed at 10 centimetres wide