Why carcinogens are not as scary as made out to be. A review of a book on the dreaded disease by George Johnson, followed by an interview with him
For a science book, George Johnson’s The Cancer Chronicles (Random House, Rs 599, 304 pages) carries the oddly philosophical message of acceptance—acceptance of the fact that cancer has been an intimate part of human existence for as long as we have walked the earth. Johnson discovers that contrary to what the media portrays, environmental carcinogens, whether pesticides or radiation, have only caused a tiny amount of cancer. Even if the hundreds of carcinogens we blame weren’t around, a minimum number of us would still develop this disease. We know this because of the evidence of carcinoma that has turned up in excavated dinosaurs and mummies from centuries ago, when there were no synthetic chemicals. Johnson, whose ex-wife fought off cancer but whose brother succumbed to it, finds comfort in knowing that cancer has always been with us, ‘that it not all your fault, that you can take every precaution and still, something in the genetic coils can become unsprung’.
Unlike Siddhartha Mukherjee’s The Emperor of all Maladies, an exhaustive account of the war against cancer over the decades, The Cancer Chronicles is a personal journey. When Johnson’s wife was diagnosed with uterine cancer ten years ago, the couple found themselves faced with a barrage of tests, confusing diagnoses and treatments. Overwhelmed, Johnson set out, perhaps too ambitiously, to make sense of the ocean of cancer research data. But wading through the statistics, he found that we know very little about cancer that is conclusive.
For example, even though the US government’s National Cancer Institute recommends eating five servings of fruits and vegetables each day, the link between eating vegetables and preventing cancer is rather weak. Further, in several cancer clusters under study where environmental carcinogens were thought to have caused higher rates of regional cancer, the alleged link was never supported by data.
Among the examples Johnson cites, readers will recognise one made famous in the Julia Roberts movie Erin Brockovich. In the 1990s, it was suspected that groundwater poisoning with hexavalent chromium was causing high rates of cancer in the California town of Hinkley. But, Johnson writes, this turned out to be a statistical illusion. Epidemiologists found that the town’s incidence of cancer was no higher than what could be reasonably expected, given the demographics of Hinkley.
Even the Chernobyl nuclear disaster did not cause as much cancer as expected. While widespread cancer was feared, two decades later, a United Nations study group estimated that less than 1 per cent of those most exposed to radiation developed cancer due to it.
But no matter what data says, when the human mind is faced with the prospect of losing a loved one to a dreaded disease, it sees patterns that do not exist. ‘All of us acquire our own personal cancer clusters, and a mental file of anecdotal evidence as unreliable as it is impossible not to deep down believe,’ writes Johnson. His own wife Nancy was an exceptionally healthy eater, eating several servings of fruits and vegetables a day, when she developed cancer. His brother Joe’s case was even more perplexing. He developed a form of mouth cancer for which he had few of the risk factors. Joe did not smoke, drank little alcohol and didn’t chew betelnut either.
Throughout the book, the poignant stories of Nancy and Joe anchor Johnson’s wanderings into the world of cancer research. He finds that there are several theories on how cancer originates, how it grows and how it can be defeated.
Each theory is much debated, so much so that cancer researchers are always working along multiples lines of research.
But as Johnson jumps back and forth between his own story and that of cancer, it is hard to miss the central message of his book. The reason cancer is so hard to beat is that it has evolved with us. It is part of the process of life, the process of cells dividing constantly and duplicating their genetic codes. Each time this happens, there is a chance of an error in duplication. This is inescapable.
In fact, such errors or mutations are the basis of life. If our genetic code were to stop mutating, life itself would stop evolving. And, paradoxically, if it were to keep mutating, we’d always be at risk of cancer.
“A certain baseline of cancer has always occurred”
Q The link between environmental carcinogens and cancer was proved in only a small number of cancer clusters. But carcinogens can affect different people differently, and their combinations can have a greater effect than individual carcinogens. Can epidemiology, which uses aggregate numbers, pick out these individual variations in how people are affected by carcinogens?
A You can imagine a situation where someone has a genetic mutation that makes them particularly susceptible to, say, chemical X, while no one else would be susceptible. There is no way epidemiology would find that. How would you know unless you had a sample of a certain size? Maybe when there are advances in sequencing the cancer genome and seeing more specifically what individual cancers look like, that would provide some clues.
It’s also possible that there are synergistic effects—someone might be exposed to a variety of different carcinogens and together it might have a significant effect. But I think in the US and other developed countries, where there have been big nationwide studies, it is fair to conclude that if cancer was being caused by these chemicals, there would be a lot more cases; it would be a lot more obvious, it would be like living near a toxic waste dump.
Also, if there is some kind of ubiquitous carcinogen and everyone is exposed to it throughout the world, how would you know that carcinogen is not incrementally increasing the cancer rate, since it would not be localised to a specific chemical or food additive? In that case, it really helps to look at what is happening with overall cancer rates over the last decades. In the US, they have been steady or going down slightly.
Q How should policy be shaped to treat minor carcinogens whose effects are uncertain and which seem to cause cancer in some lab tests but not in others?
A Of course, if there is a really clear case of something that might be a carcinogen, it should be banned or controlled. But there are very few black-and-white cases like that. There are all these carcinogens in natural foods. But no one can ban carcinogens in broccoli and spinach. You have to strike a balance in controlling toxic chemicals, but you have to consider the benefits. If there is a slight chance that a food preservative might be a carcinogen but is preventing people from getting botulism from spoilt food, you can’t ban it.
There are arguments today that no substance should be allowed in the market until it is tested and shown not to cause cancer. But how do you do that? If chemical companies do the test, people say they are biased. They say it is a function of the government. But if the government does this, a different set of people would say too much government regulation is a terrible thing.
There is a term that is very popular called the precautionary principle. It sounds wonderful, and you say, ‘Of course, this is what we should do.’ But then, you see the reality of it. There are a few outlying studies that conclude that electric power lines slightly raise the risk factor for a kind of childhood leukemia. When these studies first came out, quite a long time ago, there was a journalist called Paul Brodeur who wrote a book and a huge article in The New Yorker. Later, these studies were pretty much discounted and countered by studies that didn’t find any effect of electrical power. Then again, you can’t completely discount the possibility that electrical power lines cause cancer. And the precautionary principle would say: therefore, we need to get rid of all power lines. Or maybe bury them all underground. In an ideal world with infinite resources, it might work. In a country the size of the US and India, it is impossible. There are places in the world where people don’t have electricity and there is nothing they want more.
Some people say we should not have any processed foods and everything should be locally grown. This is completely unrealistic, unsustainable. Without technologies like artificially produced nitrogen fertilisers, there would not be enough food to feed the world. It is usually wealthy elitists who take that point of view. They are essentially asking a third to half the population to go off and die.
Q So, little is conclusively known of how cancer is caused. Do you think there will be a time when greater clarity emerges on the risk factors and treatments of cancer?
A I think we will slowly have more clarity when we study the cancer genome in greater detail. But it is very clear that there is a certain threshold level of cancer which can only be attributed to entropy, the fact that we live in a universe governed by the second law of thermodynamics. Inevitably, everything tends toward becoming disorderly. We humans call it ageing.
Robert Weinberg, the MIT cancer researcher, said, “If we all lived long enough, we’d all get cancer.” How can we have such complex systems with all these cells having to work together and not have errors? There is a certain level of cancer which will never be explained. Even if you may be able to explain it, you won’t be able to prevent it.
Q You cite statistics of cancer found in buried skeletons and mummies and state that cancer rates haven’t really increased if you adjust for age and early diagnosis. Is this an accepted view in medicine?
A Yes. With all the qualifications—if you adjust for things like the ageing of the population, the increased smoking of cigarettes and the diagnostic tools we have today, it is not controversial that a certain baseline of cancer has always occurred. Maybe there is a small additional effect from chemical and other newly introduced carcinogens.
Q Why do the American Cancer Society and other organisations prescribe a diet high in fruits and vegetables if there is no proof that it can prevent cancer?
There were early studies that seemed to show a big effect from eating fruits and vegetables on preventing cancer. But larger studies are showing that there is a very tiny effect, if any at all. But the mainstream cancer organisations never really changed their position. There is no reason to say you don’t have to eat foods and vegetables. And of course everyone wants people to remain hopeful and feel like there are things they can do. They can’t project a message of despair.
There are also many other good reasons to eat lots of fruits and vegetables. It could keep people from eating unhealthy foods and becoming obese. It certainly can’t hurt.
QYou write that there may be as many naturally occurring carcinogens as there are synthetic. Going by lab tests, we ought to be getting cancer much more often. What is protecting us?
A There is one argument that we evolved in the presence of these natural carcinogens. And therefore, some of the anti-cancer defences that our cells have developed are tuned to counteract these carcinogens. But the other argument is that even though carcinogens exist in foods, they are very dilute at the level at which they enter the human body. They only cause cancer when given in the huge doses we give laboratory animals.