There's an inescapability about cancer. It can feel more like fate than a disease. People who smoke can't help but wonder when a cell in their lungs will go rogue and produce a tumor. Living near a toxic dump gives people the sense that someone is playing Russian Roullette with their children, and sooner or later the bullet is going to fire. If you are a woman from a family of breast cancer victims, you can almost hear the clock ticking.
But we must not forget that some cancers are less like fate than they are like the flu. Take cervical cancer. It can't be blamed on bad genes or exposure to chemicals. It's caused by a virus. The human papillomavirus thrives by infecting epithelial cells. It disables their brakes, so that the cells grow faster than normal. To avoid being discovered by the immune system, HPV cloaks host cells so that they appear normal. Most people carry harmless strains of HPV. Your eyelashes are probably coated in them. They don't make the vast majority of their hosts sick because we strike a balance with the viruses. We are constantly shucking off the top layer of epithelial cells from our skin and other surfaces. Infected cells typically don't stick around long enough to cause us trouble. But every now and then, HPV will push a cell on the path to runaway growth and, ultimately, cancer.
Paul Ewald, an evolutionary biologist at the University of Louisville, thinks that we need to let this fact sink in. Most of the research on new cancer treatments goes into searching for ways to blast tumors. This is an expensive strategy that yields relatively little benefit, Ewald argues. Chemotherapy drugs can have awful side effects, and the cancer itself can adapt to the medicine through a nefarious form of natural selection. Mutations that make cancer cells more resistant to the chemotherapy take over the tumor. But if we could stop a significant chunk of cancers in the same way we battle viruses, the fight against cancer may have gotten a whole lot more promising.
In Controlling Cancer, Ewald argues that HPV is far from alone as a cancer-causing pathogen. He points to hepatitis viruses, which are known to cause liver cancer, and the bacteria Helicobacter pylori, which lives in the human stomach and can cause gastic cancer. It stands to reason, Ewald argues, that a lot of the pathogens that make us sick also push us towards cancer. For many viruses, bacteria, protozoans, and animal parasites, it pays to spur cells to replicate quickly and to evade the immune system.
If a lot of cancer is caused by infections, then we may be in a fortunate situation. We can save millions of lives with well-established measures. It doesn't take a miracle drug to block the transmission of hepatitis C, for example. Stopping people from using dirty needles will do just fine. Vaccinations could annihilate some kinds of cancer altogether.
It's a provocative idea, which is par for the course for Ewald. He's long been an advocate for putting medicine on a solid foundation of evolutionary biology. In the 1990s, for example, he came to fame for his ideas about domesticating infectious diseases. The deadliness of a parasite can evolve, and in some situations, it may pay for parasites to be milder instead of meaner. He went on to argue that many supposed chronic diseases--from heart disease to schizophrenia--are triggered by pathogens. Ewald's work has been mostly theoretical--extrapolating from what we know about evolution in general to diseases in particular. His ideas are tough to test, if only because our bodies are so complex. But they have certainly been influential, as scientists have developed better tools for detecting microbes in our bodies and probe their effects on us.
Controlling Cancer is one of the first works published by TED Books--an offshoot of the hugely popular TED talks. (Here's Paul Ewald's 2008 TED talk on domesticating disease.) TED talks are crisp, quick, emphatic, and not too heavy on scientific detail. Their books are, too. Controlling Cancer is a quick read, without any photographs, videos, or other ornaments found on other ebooks. It does include footnotes, where Ewald back up most of his points.
The citations are a good thing, but sometimes it's hard to tell when Ewald citing well-established cases of pathogens causing cancer and when he's only pointing to suggestive hints. The scientific literature is loaded with papers in which researchers describe tumors brimming with viruses. These associations could be evidence of viruses triggering cancer, or they could be evidence that tumors are good places for viruses to breed.
Ewald does point out that this ebook is just a precis of a longer book that's in the works. Controlling Cancer intrigues me enough that I look forward to Ewald making his case in full.
Carl Zimmer writes frequently about science for the New York Times and is the author of 13 books, including A Planet of Viruses