Cancer Clusters

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The study of disease clusters is one method scientists use to study the public health implications of carcinogens. A cancer cluster is defined as a greater-than-expected number of cancer cases that occurs within a group of people in a geographic area over a specific period of time. Studies of suspected cancer clusters usually focus on heredity and environment. Such clusters may be suspected when people report that several family members, friends, neighbors, or coworkers have been diagnosed with the same or related cancer(s).

In the early 1980s a leukemia cluster was identified in the Massachusetts town of Woburn. In a case that was the subject of A Civil Action, later made into a major motion picture, three companies were accused of contaminating drinking water and causing illnesses. The case went to trial in Anne Anderson, et al. v. W.R. Grace & Co., et al. Six families alleged that chemicals dumped by the defendants caused leukemia in members of those families. Two closed municipal water wells—which were the focus of the families' case—were found to be contaminated with EPA-listed hazardous substances, including trichloroethyl-ene (TCE). Although the U.S. Department of Health and Human Services (HHS) lists TCE as "reasonably anticipated to be a human carcinogen," IARC has determined that trichloroethylene cannot currently be classified as such.

In any case, this action became a poster trial for the difficulty of linking certain events to a cluster of individual illnesses. The incredibly complex case involved thirty-three plaintiffs, two defendants, a mountain of conflicting geological and medical testimony, and multiple claims including negligence, nuisance, and emotional distress. A direct and incontrovertible connection between the pollution caused by W.R. Grace and the cancer cluster was never confirmed.

The prospect of a larger cancer cluster was investigated in New York State. The Breast Cancer and the Environment on Long Island Study was carried out in response to anecdotal reports that environmental toxins elevated breast cancer rates among women in the region. Chief among the suspects were polycyclic aromatic hydrocarbons (PAH), which are caused by incomplete combustion of various chemicals including diesel fuel and cigarette smoke, and organochlorine compounds, which are found in many pesticides. In

Comparison of a smoker's lung (r) to a normal lung (l). (Photograph by A. Glauberman. National Audubon Society Collection/Photo Researchers, Inc. Reproduced by permission.)

August 2002 scientists reported that organochlorine compounds were not associated with the elevated rates of breast cancer on Long Island. However, the same investigators did suggest it was possible that risk in some individuals may be associated with organochlorine exposures because of individual differences in metabolism and the ability of one's body to repair DNA damage.

The researchers also found that PAHs were associated with a modest 50 percent increased risk for breast cancer in susceptible women exposed to high levels of the compounds. But for the population of women as a whole, no specific environmental factor could be tied to the incidence of breast cancer. Some have complained that the study failed to take into account the possible effects of leaks from a nearby nuclear reactor, and there have been public accusations that the study avoided the so-called "nuke connection" for political and financial reasons.

The thousands of individuals who were in and around the World Trade Center in lower Manhattan on and immediately after September 11, 2001, may constitute a cluster of future disease. Public safety personnel, rescue workers, and local residents were exposed to a lingering pall of dust and debris following the collapse of the twin towers and other buildings. Superheated and aerosolized building materials created an incalculable number of toxic compounds. The full effects on the health of those exposed may not be known for decades.

In conclusion, the interplay between our environment and cancer is complex and not yet fully understood. It is increasingly clear that the unborn and very young children are particularly susceptible to environmental toxins such as endocrine-disrupting herbicides and insecticides. Adult cancer risk can be greatly reduced by avoiding tobacco products and limiting sun exposure. Known carcinogens often encountered in workplaces and homes include pesticides, asbestos, arsenic, uranium, and certain petroleum products. see also Asbestos; Health, Human; PCBs (Polychlorinated Biphenyls); Radon; Risk.

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