Invading the body
Most normal cells in your tissues stay put, stuck to each other and their surroundings. Unless they are attached to something, they cannot grow and multiply. If they become detached from their neighbours, they commit suicide, by a process known as apoptosis. But in cancer cells the normal self-destruct instructions do not work, and they can grow and multiply without being attached to anything. This allows them to invade the rest of the body, travelling via the bloodstream to start more tumours elsewhere (metastasis).
