Unlike Ebola, flu or polio, cancer is a disease that arises from within — a consequence of the mutations that inevitably occur when one of our 50 trillion cells divides and copies its DNA.
Some of these genetic misprints are caused by outside agents, chemical or biological, especially in parts of the body — the skin, the lungs and the digestive tract — most exposed to the ravages of the world. But millions every second occur purely by chance — random, spontaneous glitches that may be the most pervasive carcinogen of all.
It’s a truth that grates against our deepest nature. That was clear earlier this month when a paper in Science on the prominent role of “bad luck” and cancer caused an outbreak of despair, outrage and, ultimately, disbelief.
The most intemperate of this backlash . . . suggested that the authors, Cristian Tomasetti and Bert Vogelstein of Johns Hopkins University, must be apologists for chemical companies or the processed food industry. In fact, their study was underwritten by nonprofit cancer foundations and grants from the National Institutes of Health. In some people’s minds, those were just part of the plot.
What psychologists call apophenia — the human tendency to see connections and patterns that are not really there — gives rise to conspiracy theories. It is also at work, though usually in a milder form, in our perceptions about cancer and our revulsion to randomness.
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For a handful of cancers, biological agents are important, like human papilloma virus in cervical cancer and helicobacter pylori in stomach cancer. . . .
[And] heredity — like the BRCA mutations involved in some breast cancers — can have a profound effect in individual cases. But inheritance appears to be involved in just 5 to 10 percent of all cancers.
What that leaves is a large role for random, spontaneous mutations — the ones that just happen because of the microscopic grind of life.
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[T]the authors looked at stem cells — those that are capable of dividing indefinitely and renewing themselves. First, they estimated the number of these cells in different tissues of the body and how many times they would copy themselves during a human lifetime. The higher the count, the greater the vulnerability to mutations.
Then they compared that number with the likelihood that a tissue would develop a malignant tumor. The result was a strong correlation, a steep sloping line suggesting that two-thirds of the difference in cancer susceptibility could be explained by spontaneous errors.
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For cancers like those of the bone and brain, chance seemed to rule. But at the other end of the spectrum were those that were more “deterministic” — like lung cancer and basal cell carcinoma, a usually harmless skin malignancy where sunlight plays a deciding part. . . .
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It is always possible that what we call randomness will turn out to be complexity in disguise. Some mutations attributed to chance may eventually be revealed to have subtle causes.
Over the years, however, the scale seems to be tipping the other way, with the discovery that some long-suspected agents like dietary fat and artificial sweeteners may not be so potent after all.
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