Most people prefer to bury their heads in the sand rather than think about the risk of cancer. But habits and lifestyles picked up when young have a big impact in later life. Vicky's fear of breast cancer is so acute, she's had a double mastectomy to reduce her chances; confirmed smoker Darius finds out just what the poisonous chemicals are doing to every organ and tissue in his body; and John makes good use of a pile of wooden building blocks to explain just what happens when a cell becomes cancerous.