Cancer Clusters: Findings Vs Feelings

David Robinson

Disclosures
In This Article

A Case in Point -- Long Island and Breast Cancer

One example of how science can be overtaken by public concern can be found in the ongoing investigation of breast cancer rates on Long Island. Several advocacy organizations have sprung up to urge public health authorities to take action regarding a perceived breast cancer "epidemic." The oldest of these groups is 1 in 9: The Long Island Breast Cancer Action Coalition. Operational since 1990, 1 in 9 (along with the similar groups that have since been created) serves as a highly effective force in the public debate. 1 in 9's Web site explains: "we have organized and participated in trips to Albany and Washington to educate our legislators about the need for action that will help prevent the breast cancer epidemic."[22]

1 in 9 has tenaciously supported the idea that industrial pollution is elevating the rates of breast cancer on Long Island. Geri Barish, the group's president, wrote an instructive editorial in response to claims that her group was doing more to stoke fears than to support science:

As activists, we are motivated by an absolute and unflinching commitment to examine every possible scenario for the unacceptably high levels of cancer in our midst. While we recognize that many factors, including genetics, diet, and poor health practices contribute to the rates of the disease, we believe that industrial chemicals, such as pesticides and other environmental contaminants, may also play a role.[23]

One breast cancer victim, voicing concerns typical of those recorded by news media, seems convinced that pesticide use on neighboring lawns caused her cancer. Noting that her neighbors want "their lawns green and bug-free," she feels the fact that 3 women on her block have died from cancer is "not a coincidence. It can't be."[24] Concerns like these highlight the quandary in which public health officials find themselves -- they cannot, no matter how much they investigate, prove that the elevated rate is a coincidence, even if that is the real explanation, because it is not possible to prove a negative.

Ms. Barish and her colleagues do not appear to consider it a possibility that, when known breast cancer risk factors such as Jewish ethnicity, bearing a first child later than usual in life, socioeconomic status, early age at menarche, and late age at menopause are considered, the rates of cancer on Long Island might be no higher than should be expected. Geography might be symptom rather than cause, because people who live on Long Island tend to share other characteristics beyond area of residence. Any cancer, anywhere, deserves the attention of medical professionals. The question is whether the number of breast cancer cases on Long Island suggests that Long Island should get more attention than other localities, breast cancer more attention than other diseases, or the environment more attention than other potential risks. The answers to these questions might be no -- a possibility that 1 in 9 does not consider.

1 in 9's legislative activism, combined with that of other Long Island breast cancer groups, succeeded on June 10, 1993, when the US Congress passed a bill mandating an investigation into possible environmental causes for breast cancer on Long Island by the NCI. The bill, which was supported by then-New York Senator Alfonse D'Amato, explicitly required the NCI to examine 5 possible environmental risk factors -- "contaminated drinking water, sources of indoor and ambient air pollution, electromagnetic fields, pesticides and other toxic chemicals, and hazardous and municipal waste."[25]

Thus, the power of public pressure was responsible for getting an investigation launched. This intervention by activist groups is often counterproductive because it has the effect of circumventing the normal mechanisms that guide scientific inquiry. By creating a narrowly tailored federal mandate to investigate putative environmental causes of breast cancer, advocates and legislators have taken over a task for which scientists are the most qualified -- deciding how limited research and public health dollars ought to be spent.

The Long Island breast cancer issue also provides a demonstration of the "bull's-eye" problem. An article in Newsday entitled "Waiting for Science Can Cost Lives" celebrated the day when "the determined and creative women of Long Island went door-to-door and began plotting cases of breast cancer in the area."[26] As discussed above, the increased scrutiny to which the area under study is subject may create an inaccurate impression of an elevated cancer rate.

The mandated investigation, called the Long Island Breast Cancer Study Project (LIBCSP), is ongoing. The findings released thus far, available to the public at the Project's Web site,[27] do not seem to bear out the fears of community activists.

One of the questions at the core of this debate is whether breast cancer rates on Long Island are elevated at all, and if they are, whether this elevation can be explained in terms of nonenvironmental risk factors like those outlined above. The LIBCSP has just released a comprehensive Geographic Information System designed to help researchers investigate the situation. Meanwhile, using already available tools, a group of researchers at the NCI completed a study, "Breast Cancer Clusters in the Northeast United States: A Geographic Analysis."[28] Taking pains to avoid the bull's-eye problem discussed above, the researchers used a computer modeling system to scan the study area for significant clustering. They found that "there is a statistically significant and geographically broad cluster of breast cancer deaths in the New York City-Philadelphia, Pennsylvania, metropolitan area" and noted that within this large cluster are 4 smaller clusters, each significant in its own right -- Philadelphia with suburbs, central New Jersey, northeastern New Jersey, and Long Island. The researchers explained: "the elevated breast cancer mortality on Long Island may be viewed less as a unique local phenomenon and more as part of a more general situation involving large parts of the New York City-Philadelphia metropolitan area." This study thus confirms that rates on Long Island are elevated, but does not do so in a way that lends support to theories about localized pollution causing cancer, since it examines such a broad area. Whether the use of pesticides in a neighborhood or proximity to power lines or to a factory (or any similar situation) is responsible for the elevated rates cannot be determined from a study that considers such large aggregates of people. It is worth noting, however, that the cluster identified by the study extends well beyond Long Island. The area of the cluster does not share proximity to any single source of industrial pollution. Many activists have pointed to the Long Island aquifer, which is the source of drinking water for all Long Island residents, as a potential risk because of seepage of chemicals into the aquifer from the ground. The identified cluster, however, includes many sources of drinking water other than the Long Island aquifer, suggesting that water contamination is likely not the reason for the increased risk.

Looking at these data, the researchers concluded that the high breast cancer risk is likely due to one of the factors that they were not able to incorporate in their study. "The several known and hypothesized risk factors for which we could not adjust that may explain the detected cluster are most notably age at first birth, age at menarche, age at menopause, breastfeeding, genetic mutations, and environmental factors," they wrote. They group "known and hypothesized" risk factors together, but it is important to differentiate between the two -- environmental factors are a "hypothesized" source of risk. For example, the author of a paper entitled "Epidemiology of Breast Cancer: An Environmental Disease?" explains that the goal of the paper is to consider "potentially controversial conditions which could in the future be recognized as new risk factors."[29]

An in-depth study of the two most frequently blamed chemicals, the pesticide DDT and an industrial insulator called PCBs, investigated Long Island women and concluded that increased risk of breast cancer does not appear to be associated with past exposure to these compounds.[30] Further, the study's authors found that "breast cancer risk among Long Island residents was not elevated compared with residents of the adjacent New York City borough of Queens."[30] Some smaller-scale studies completed in the early 1990s had indicated that PCBs might be a cancer risk, but these results were not confirmed by this LIBCSP study.

The investigation mandated by the 1993 law funded 5 separate large US studies of women located mainly in the northeastern United States, to evaluate the association of blood and serum levels of DDE (a chemical produced as DDT breaks down in the environment) and PCBs with breast cancer risk. In a review of these 5 studies published in the Journal of the National Cancer Institute, researchers concluded that "combined evidence does not support an association of breast cancer risk with plasma/serum concentrations of PCBs or DDE. Exposure to these compounds, as measured in adult women, is unlikely to explain the high rates of breast cancer experienced in the north-eastern United States."[31]

Another area the LIBCSP is investigating in response to the congressional mandate is the possibility of carcinogenic effects from electromagnetic fields. A research group at the State University of New York at Stony Brook conducted a review of occupational studies evaluating correlation between women's workplace exposure to electromagnetic fields and the incidence of breast cancer. They reported that 11 such studies have been conducted. Six of the studies found no association between cancer and workplace exposure, 3 of the studies found an association for the whole group studied, and 2 of the studies revealed associations only in subgroups of the population under study.[32] When an association represents a causative relationship, studies are much more consistently positive.

The LIBCSP's largest, definitive report has yet to be published. Based on the findings released thus far, however, it seems that the political impulse to tie breast cancer on Long Island to industrial pollution is not being validated by science.

None of the studies conducted to date establish that trace amounts of industrial pollution diffused in the environment are causing cancer clusters. This could change as the issue receives continuing scientific scrutiny. For now, however, there is a substantial gap between scientific findings on this issue and public perceptions. Science continues to indicate that the primary sources of cancer risk are obesity, diet, exercise, smoking, alcohol, sun exposure, occupational chemical exposure, genetic familial cancer syndromes, and susceptibility risk factors such as infectious agents -- and not environmental chemical exposure. Beyond these, chance (random case clustering) is a major predictor of perceived cancer clustering. Citizens, journalists, and public officials share in the responsibility for accurate and fact-based discussion.

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