Thursday, November 7, 2013 |
Almost every one of us has been touched by cancer, directly or indirectly. About 10 years ago, the disease touched American science writer George Johnson, when his wife at the time (they are no longer together) was diagnosed with an aggressive form of uterine cancer. This spurred him to find out all he could about cancer -- and what he found, for the most part, was that we generally misunderstand what causes it, and why it's so hard to cure. Johnson documents his search for answers in his latest book, The Cancer Chronicles: Unlocking Medicine's Deepest Mystery. In a recent interview on Quirks & Quarks, he shared some of what he had learned in the course of researching and writing the book.
Johnson told host Bob McDonald that his wife's diagnosis was a surprise in part because "she did everything right." She ate a healthy diet, and exercised regularly. The diagnosis was a rare cancer that is almost always fatal (though she survived).
There's a general perception that cancer is affecting more and more people. But statistics don't back that up, according to Johnson. "The general overall rate of cancer in the developed world, and really worldwide, is no greater than it was in the past," he said. "In fact, it's remained steady for decades and has been slightly declining with very few exceptions." He added that the incidence of the most common forms of the disease, namely breast cancer, prostate cancer and colon cancer "has been declining for decades."
This seems to contradict the notion that there's a link between the disease and exposure to chemicals in our environment. Johnson pointed out that in fact cancer is actually the result of a natural process that goes wrong. "The human body consists of about 10 trillion cells of different kinds, and they have to work in harmony," he explained. "Cancer is caused when one of these cells, and then its children, undergo some changes that causes it to lose touch with the rest of the crowd." These cells begin to multiply "like crazy" and attack healthy cells. Johnson went on describe these random mutations as "almost like some kind of quasi-creature that's trying to evolve inside the ecosystem of your body."
But what causes cells to undergo these mutations? Johnson said that 30 per cent of cancers are caused by smoking cigarettes, and another 30 per cent of cancers are related to diet. But he added that epidemiology hasn't been able to prove that specific foods are good or bad. He also noted that carcinogenic chemicals account for only a few percent of cancers. The idea that cancer can be triggered by the environment persists. But Johnson cited the case of Love Canal, a neighbourhood in Niagara Falls, New York, which was revealed as a toxic waste site in the mid-1970s. Three decades later, epidemiological studies found that the cancer rate was no higher for people there than for the general population, and was actually slightly lower.
This finding made Johnson rethink the idea that cancer has an external cause. "Really the most powerful carcinogen is entropy," he said. The cells of our bodies are constantly dividing, and it's inevitable that there will sometimes be errors. Some of those mistakes will lead to the child cell dying, or the mistakes of the DNA will be repaired, or harmless. "The vast majority are random copying errors. In that sense, randomness is the main cause of cancer."
In his book, Johnson compares the growth of a cancer tumour to how a fetus grows in the womb. "Natural processes are co-opted in a sense by the cancer cell," he said.
Cancer is also an unavoidable effect of evolution. "The reason we've evolved is because our cells are able to mutate," Johnson said. Beneficial mutations are part of the process of natural selection, and have driven our development as a species. If cell replication was always perfect, mutations wouldn't occur -- but neither would evolution. "It's an evolutionary trade-off."
Johnson was struck most by the randomness of cancer. "You can do everything right. You can live your life in all the ways that are said to be the healthiest choices, and still, for random reasons, you can get cancer," he said. He went on to say that it's human nature "to look for a cause and a reason for everything. But often there aren't causes, and in most cases of cancer, there really isn't a known cause and there probably never will be."