Why do we focus on the least important causes of cancer?
A grim report released this week by the President's Cancer Panel warns of "a growing body of evidence linking environmental exposures to cancer." Despite its frightening pronouncements that modern-day life is poisoning us, many observers, including the American Cancer Society, are dismissing the report as flawed and, at worst, alarmist. The report's "conclusion that 'the true burden of environmentally (i.e. pollution) induced cancer has been grossly underestimated' does not represent scientific consensus," the ACS says. In 2008, Slate's Darshak Sanghavi warned against overestimating the cancer-causing potential of chemicals, power lines, cell phones, and other popular villains. "It's distracted us from the uncomfortable truth that most cancers are caused by the natural environment around us," he wrote. His article is reprinted below.
Last month, the London Independent ran a sensationalist story about cell phones causing brain tumors, and the Breast Cancer Fund released a comprehensive report on carcinogenic chemicals women should avoid. Other recent cancer-causing culprits in the news include pesticides, power lines, and solvents.
This thinking cleaves to a popular motif: The natural world is less toxic and more healthful than the industrial one. To avoid cancer, you should buy organic produce, drink unpasteurized milk from specialty dairies, eat more fiber to cleanse the colon of carcinogens, and avoid cheap cosmetics. To protect one's family, in short, become a paranoid consumer of everyday "artificial" products.
Unwittingly, we've seriously impeded cancer prevention with this not-so-useful distinction between the natural and artificial. It's distracted us from the uncomfortable truth that most cancers are caused by the natural environment around us. As a result, we expend great effort and ink on low-yield strategies to prevent cancer, even though the better ones lie within our grasp.
Take the popular example of asbestos, which is associated with a rare form of lung cancer called mesothelioma. Everyone knows asbestos is dangerous, and litigation related to the hazardous material is one of the longest-running U.S. tort actions in history (costing $70 billion, according to a RAND analysis). Yet the Centers for Disease Control and Prevention report only about 2,000 cases of mesothelioma per year, of which only a fraction can be attributed to previous asbestos exposure.
Or take diethylstilbestrol, known as DES, a drug used to promote fertility in certain women until it was shown to cause genital cancers in a blast of publicity in 1971. Ultimately, fewer than one in 1,000 exposed women got these cancers. Or consider the plant-ripening agent Alar, which was voluntarily withdrawn in 1989 after the American Academy of Pediatrics called for a ban and a 60 Minutes report blamed it for cancer risks. No data have ever actually shown Alar to be harmful to humans. And today no European country fortifies flour with folic acid, in part because of the unlikely possibility that the vitamin could cause colon cancer. As a result, many babies in Europe continue to be born with spinal defects, which the extra folic acid would prevent.
Of course, the women who endured genital cancers from DES or the asbestos workers who came down with mesothelioma deserve sympathy. But the dominant strategy of cancer prevention to which the DES and asbestos scares led—one-by-one alarmist publicizing of man-made carcinogens, regardless of their relative importance—is unlikely to make any serious dent in cancer rates. After all, half of all chemicals are carcinogenic in laboratory tests. A smarter strategy would simply focus on the most preventable exposures causing the most malignancies, without any regard for what's natural and what's man-made.
To begin with, that means paying more attention to common infections. Most women today are infected with human papilloma virus, which is a necessary precondition for about half a million cervical cancers worldwide (not to mention anal, penile, pharynx, and even skin cancers). These numbers dwarf those associated with DES exposure. To prevent HPV infection—and later cancer—people must be vaccinated before their sexual debuts, preferably as pre-adolescents. Yet several state legislatures have withdrawn bills encouraging vaccination, and fewer than half now have school-based requirements for HPV vaccination.
According to the CDC, roughly 50,000 Americans in 2006 were infected with hepatitis B, a key cause of liver cancer, despite the availability of a safe and effective vaccine. And the world's second-leading cause of cancer deaths (subscription required)—stomach malignancies—may largely result from an infection by corkscrew-shaped bacteria called Helicobacter pylori, which infects up to two-thirds of the world's population. No effective vaccine yet exists, but an intriguing 2004 study showed that treating the infection with cheap antibiotics in highly selected patients can eliminate future gastric cancers. Though well-designed, that study was in China, and no similar American research has been done. As a result, no clinical guidelines to prevent gastric cancer from the infection exist here.
Another "natural" cancer cause has a fix that's not a vaccine. According to the CDC, almost 5 billion humans are at risk of aflatoxin exposure. Never heard of it? It's a natural product of mold that grows in peanuts, grains, and milk—and like hepatitis B, a leading cause of liver cancer. Strategies to reduce the toxin, like proper crop storage, genetic engineering to produce resistant plants, and regular food testing, could save thousands upon thousands of lives. But they are underutilized and underfunded in much of the developing world.
With dubious links between cancer and cell phones offered as worry candy, we forget about more important natural environmental causes of cancer like sunlight, which is clearly linked to deadly melanomas. For years, manufacturers have touted the anti-cancer benefits of sunscreen (including a series of full-page magazine ads last year). * How many people realize that the principal cause of melanoma is UV-A radiation, which isn't blocked by many sunscreens? * The Food and Drug Administration doesn't even consider UV-A in its labeling requirements for the product.
The obsession with man-made toxins not only reflects a small-minded view of cancer's causes but hints at a worrisome theme in American public health. Our scattershot approach to preventing cancer subscribes to the cult of personal responsibility, albeit with a recent eco-friendly twist: To really help themselves, goes the thinking, people must simply take charge of their health and avoid cancer-causing, artificial products. Somewhat insidiously, we're starting to believe that cancer mostly is prevented by informing individuals to change their consumption habits—not by proactive, broad-based public-health measures like widespread vaccination or agricultural reform.
For example, we could continue worrying about the unlikely link of folic acid in bread with colon cancer and tell people to buy unfortified bakery goods. Or we could remember that a regular colonoscopy for Americans over 50 could drop colon cancer deaths from current levels by 60 percent and figure out why fewer than half of Americans get them. To lower breast cancer rates, we could tell women to buy hormone-free cosmetics or refrain from using deodorant. Or we could encourage mammography and further study medications like raloxifene, which may prevent breast cancer in selected high-risk women.
In the end, admitting that most cancers have natural causes rightly shifts the focus on cancer prevention away from individual consumers. That's a good thing, since in the end, you can't always shop your way to becoming cancer-free.
Correction, April 16, 2008: The original sentence incorrectly stated that the ad ran recently in the New York Times. (Return to the corrected sentence.)
Darshak Sanghavi is Slate's health care columnist. He is chief of pediatric cardiology and associate professor of pediatrics at the University of Massachusetts Medical School as well as the author of A Map of the Child: A Pediatrician's Tour of the Body. Follow him on Twitter.