By George Johnson
Lay a chessboard on a table. Then grab a handful of rice and let the grains fall and scatter where they may. They won't spread out uniformly with the same number occupying each square. Instead there will be clusters. Now suppose that the chessboard is a map of the United States and the grains are cases of cancer.
Each year about 1.6 million cases of cancer are diagnosed in the United States, and epidemiologists regularly hear from people worried that their town has been plagued with an unusually large visitation. Time after time, the clusters have turned out to be statistical illusions — artifacts of chance.
The Erin Brockovich incident, one of the most famous, is among the many that have been debunked. Hexavalent chromium in the water supply of a small California town was blamed for causing cancer, resulting in a $333 million legal settlement and a movie starring Julia Roberts. But an epidemiological study ultimately showed that the cancer rate was no greater than that of the general population. The rate was actually slightly less.
Of the handful of residential clusters that have not been dismissed as flukes, only two in the United States have been associated, with a great deal of uncertainty, with environmental contaminants. Both involved childhood cancer. One was found in the 1980s in Woburn, Mass. The other was found about a decade later in Toms River, N.J., and is the subject of an absorbing new book by Dan Fagin, a former reporter for Newsday and the director of the science, health and environmental reporting program at New York University. I first read it in manuscript about a year ago, and I've been puzzling over it ever since.
We're not talking about thousands of cancer cases unleashed in a town by industrial poisons. Or hundreds. Cancer clusters occur on a far smaller scale. An early study of Toms River in 1995, as suspicions were beginning to grow, found a total of 56 childhood cancers in the township (population 76,000) over a period of 13 years. Based on figures for the whole state, 43 of those cases might have occurred anyway. They were part of the normal background rate, cancers that may happen for no apparent reason.
In the central part of Toms River, there were 14 childhood cancers during those years when between nine and 10 would have been expected. But however closely you analyzed the cases, it was extremely difficult — and maybe impossible — to distinguish the blips in the data from what could have occurred by chance. For the children and their parents these were not blips but tragedies. They naturally wanted an explanation. Something or someone to blame.
Fagin was just finishing "Toms River: A Story of Science and Salvation" when I met up with him at a journalism conference last spring. At a reception one evening, we came to realize that we both were writing books about cancer that would be published this year. (My book, "The Cancer Chronicles," is scheduled for August.) Later, as we read and commented on each other's drafts, we were struck by how we saw the issue of cancer and the environment in very different ways.
Toms River is a story of determined parents forcing reluctant government officials to persist until they found a plausible source for their children's illnesses. But as I read and reread the book, I couldn't shake the feeling that the bigger story was how human grief can drive the brain to see cause and effect whether or not it's really there. After five years and an investigation that cost more than $10 million, it is not certain that anyone in Toms River got cancer from toxic waste discharged by local companies into the atmosphere. The frustrating thing about the science of cancer is that we will probably never know.
Whether you look on the community or the molecular scale, cancer is largely a matter of chance. Every second, millions of cells in a body are copying their DNA as they prepare to divide. It is an imperfect process, and errors occur at every turn. Some are corrected, some are not, and every once in a while the right combination causes a cell to begin multiplying indefinitely, bringing forth a malignant tumor.
Many chemicals, natural and synthetic, can damage DNA and increase the background mutation rate. But most cancers require several genetic hits — whether they are spontaneous, inherited, or induced from outside. Cancer clusters have been verified among workers who are exposed for years to high levels of carcinogens such as asbestos. The hits just keep on coming. But even occupational clusters are rare. One study after another has concluded that the relatively dilute exposures received by the public are probably not causing much cancer, even in places near toxic waste dumps, like Love Canal.
Toms River, like Woburn, appeared to be an exception. But was the difference caused by two federal Superfund sites that had been polluting the area for years? Or was it a statistical anomaly? Years earlier, the epidemiologist Seymour Grufferman coined the term "Texas sharpshooter effect." Stand way back and blast the side of a barn with a shotgun and then find some holes that are crowded together. Draw a circle around them and you have what looks like a bull's-eye.
When New Jersey officials concluded that there was probably nothing to worry about in Toms River, angry residents stormed the county health department. As the pressure continued, the state joined federal epidemiologists in a full-blown investigation. Interviews were conducted. Birth records were studied. Computer models were made of the water system and of the paths toxic emissions might have followed through the air. DNA was tested, and effluents were analyzed.
As epidemiologists worked through the data, they were struck by a pattern of evidence that appeared to implicate one of the town's polluted well fields. But given the small number of cases, the uncertainty was overwhelming. In the end, two correlations seemed to rise above the rest — but only when boys were excluded from the statistics. That left eight girls whose mothers had drunk most often from the well field. Five of the girls had leukemia, a cancer of the blood, and three did not. The boys were apparently unaffected. A similar association was suggested for leukemia in girls with prenatal exposure to polluted air. For the other types of cancer a link to environmental contaminants couldn't be established.
So what are we to make of this? As epidemiologists parsed the numbers this way and that — including one age group in their calculations and excluding another, or making different assumptions about when contamination reached the water taps — were they closing in on a deeply hidden truth or picking and choosing among the data? There was no biological explanation for why male and female fetuses would respond differently to the carcinogens. If limiting the analysis to girls hadn't uncovered an association, would the next step have been to distinguish between those with brown hair and blond?
The study ultimately concluded with "considerable uncertainty" that water and air pollution might have been risk factors for leukemia in prenatally exposed girls. As with Woburn, the evidence was ambiguous and the litigation was settled out of court. The polluters paid off the plaintiffs while denying blame, and the families were left feeling robbed of vindication.
Given those kinds of subtleties and an anticlimactic ending, it takes a good writer to tell a compelling tale. With a talent for describing courtroom drama, Jonathan Harr turned the Woburn case into a best-selling book, "A Civil Action." Where Fagin excels is in vividly recounting the science of carcinogenicity and the remarkable history of how the international chemical and pharmaceutical industry arose from a few Swiss dye makers — along with the problem of pollution and the ever inexact science of epidemiology. He brings the complexities of Toms River to life. The result is an honest, thoroughly researched, intelligently written book. It closes with the warning that there may be more to Toms River than what could be confidently concluded from the data — and other towns where industrial pollution is causing a barely noticeable but deadly rise in cancer.
That may be, but no matter how hard I squinted at the numbers, I found it hard to be convinced that there had been a cancer problem in Toms River. The tools of statistics, so powerful when applied to large populations, break down with small numbers. As so often in life, we're left wondering how to distinguish between randomness and patterns too subtle to see.