Cancer cells are, for all intents and purposes, immortal. Having broken free of the rules and strictures that govern other cells, they are free to grow and divide as they please. In a short space of time, a lone cancer cell can form a mass of identical clones – a tumour. Often, these grow and spread quickly at the expense of their host who usually ends up dying, taking the tumour with it. But there is one way a cancer could escape this fate and carry on its selfish reproduction – by finding another host. It could become contagious.

In humans, cancers are definitely not contagious. You can’t catch cancer from someone who has it; at most, you can inherit a