Breast cancer cells. Coloured scanning electron micrograph (SEM) of dividing breast cancer cells. Cancer cells divide rapidly and chaotically, and may clump to form malignant tumours. The tumours often invade and destroy surrounding tissues. Breast cancer is the most common form of cancer in women. Treatment involves surgical removal of the tumour, often combined with radiotherapy and chemotherapy. Magnification: x5000 at 6x7cm size.