Having looked at some of the basic facts, and indeed non-facts, of cancer it’s tempting to go straight to the really exciting bits, namely the extraordinary molecular events that underpin the way animals work and the astonishing science that is gradually revealing what can go wrong to give rise to diseases in general and cancers in particular. However, before we indulge ourselves, perhaps we should pause for a moment to consider the question ‘Why is cancer so important?’ Well, you might answer, ‘Because it kills a lot of us.’ True indeed, but it transpires that it’s well worth a bit of time and effort looking into that answer – and that means looking at a few facts and figures or, to make it sound even more off-putting, at the statistics of epidemiology. Before you run a mile on the grounds that maths makes your head ache, let me implore you to stay a while. I promise it will be worth a little pain, and the reason I’m so confident is that the facts of cancer, the sheer numbers, are so staggering, so mind-bogglingly overwhelming, that they begin to tell us something about the underlying causes of the disease.