Paul Ehrlich’s pursuit of drugs to combat infectious diseases led him to the notion of a ‘magic bullet’ – something that could kill microbes such as bacteria without any harm befalling the infected individual. He also came up with the word ‘chemotherapy’ to mean the use of chemicals to treat disease. Having chronicled the rise in the profile of microbiota in cancer, it might be informative, at the outset of this chapter, to refer to a striking demonstration of the challenge presented by bacteria because it has a strong parallel with cancer.

We began our cancer odyssey with perhaps the most frequently asked question, ‘What causes cancer?’, and the shortest reply: ‘Mutations’. But that’s a biologist’s answer. What we really want to know is ‘How?’ How do these changes come about and, of course, what can we do about them? Broadly speaking, two categories have been long-recognized as the underlying causes of cancer – ‘hereditary’ and ‘environmental’. The former refers to the state of our DNA when we get it – mutations passed to us at birth kick off about 10 per cent of all cancers. The second group includes everything else and in doing so lumps together things that we can’t control (e.g., radiation from the ground) with those we can (e.g., smoking). The latter really should include a sub-group: ‘self-destruction’ perhaps.

Once upon a time it was fair to say that most people knew little of science. After all, scientists spent years learning their job so it’s clearly tough-going and, by and large, the rest of the world could get by knowing nothing of superconductivity or the origins of the universe. But increasingly our daily lives have come to be dominated by science, and part of that revolution has been the ever-expanding reach of television and the Internet as sources of information. It’s as though, unwittingly, we’ve all signed up to the Open University. And, it should be said, when it comes to science this has all been helped by a growing awareness among those in the trade that they have an obligation to let the world know how they while away their days.

We have already encountered the seventeenth-century scientific genius Robert Hooke giving mankind his first glimpse of the miniature world of cells. It seems likely that Micrographia, his book of illustrations, came into the hands of one Antonie van Leeuwenhoek, the proprietor of a drapery business in Delft in the province of South Holland. In his spare time Leeuwenhoek had taught himself how to handle glass and he became so skilled that he was able to make the first compound microscope – one using two lenses that could magnify objects several hundred times. He started to look at animal cells and, in 1677, became the first person to see single red blood cells and sperm cells. He went on to discover bacteria, thereby making himself the first microbiologist. Through these technical advances, Leeuwenhoek changed the world by enabling scientists to look at individual cells, setting us on the road to understanding what we now simply accept as a fact of life – that all animals and plants are clumps of cells. Few outside science would recognize Leeuwenhoek’s name today, which is slightly sad and somewhat ironic, given that his lifelong friend, the artist Vermeer, is world-famous.

In the opening ‘question and answer’ chapter we blithely asserted that most folk know that genetic material is made of DNA – the stuff of heredity – and that it is damage to DNA (mutations) that cause cancer. As we noted, these gigantic molecules are made up of huge numbers of four small chemical units (the bases A, C, G and T), linked together in two chains. In humans there are about 3,000 million bases in each chain. It is the sequence of these letters in DNA that forms a code telling the cellular machinery which proteins to make – proteins being the things that do all the work and hence make individual cells and animals what they are.

The story of cancer began hundreds of millions of years ago and has continued in parallel with mammalian evolution. However, it only became a scourge in the twentieth century, mainly due to the doubling of the human lifespan. The era of molecular biology began in the second half of that century and this has unveiled much detail about the behaviour of cells and what goes wrong when they proliferate in an abnormal manner – the basic cause of cancers.

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.

Following the controllables, we come to things we either cannot control or are difficult to regulate, together with accidents and some dark episodes that are also part of the cancer story.