Writing in Reason, Ronald Bailey has a nice look at the so-called Long Island Cancer Cluster and a recent study designed to find out why so many women in and around Long Island have breast cancer. After spending several years and $8 million, the National Cancer Institute study concluded that whatever might be contributing to the cancer cluster, it isn’t exposure to chemicals and pesticides in the Long Island area.
Research into breast cancer in Nassau and Suffolk counties in Long Island found that women there had rates of breast cancer that were roughly 3 percent higher than the rest of the nation. Some breast cancer advocates were convinced that the only possible explanation for the higher rate was due to chemicals in the area.
But a study of blood and urine from 3,000 women in the Long Island area found no evidence for this hypothesis. The study looked at levels of DDT, PCBs, chlordanes and chemicals indicative of cigarette smoking. The bottom line — women exposed to such chemicals were no more likely to develop breast cancer than women not exposed to such chemicals. This result was consistent with other studies such as an almost 33,000 patient study published in the New England Journal of Medicine in 1997 that found no evidence that exposure to DDT or PCB increased the risk of a woman developing breast cancer.
Why would advocates focus on DDT, PCBs, chlordanes and other chemicals? In part because those chemicals have all been found to be carcinogenic in mice, rats and other laboratory animals. Now animal tests are helpful in identifying substances that are potentially harmful to human beings, but they are not the last word. Some substances that are harmful to laboratory animals are perfectly safe in human beings, while some substances that do not harm mice or rats are nonetheless very harmful in human beings. Merely because animal tests indicate that a substance is likely to be carcinogenic does not mean that it actually is in human beings.
But that seems to be the message that some people are taking away from media reports on such research. The New York Times, for example, quotes Geri Barish, president of 1 in 9: The Long Island Breast Cancer Action Coalition, as wondering how, if these chemicals are carcinogenic in animal tests,
How could they absolutely say that a known carcinogen is not absolutely involved in the cause of cancer? . . . I refuse to accept the fact that they didn’t find anything. They didn’t find anything conclusive because in the scientific world it has to be exact.
Barish wants further studies to be done, but Dr. Barbara Hulka, a professor of epidemiology at the University of North Carolina, told The Times that so many studies have already been done looking for a link between DDT, PCBs and breast cancer that there may be nothing more to learn there. Hulka told The Times
I think it is important that these studies have been done. . . [but] There comes a point after so many studies are done that it becomes less productive to continue that line of work.
There have been so many epidemiological studies of DDT and PCBs, for example, that if they really caused or contributed to breast cancer one would think that at some point this would show up clearly in such studies. But in fact, all of the large studies of these chemicals have so far found no statistically significant connection between chemicals and cancer.
Perhaps it is time to recognize that cancer clusters are always going to occur largely because cancer is never going to be evenly distributed throughout a population, and begin taking the millions of dollars that have been devoted to looking at cancer clusters and spending it on more fruitful avenues of research.
Sources:
Looking for the link. Gina Kolata, The New York Times, August 11, 2002.
Cluster bomb. Ronald Bailey, Reason, August 14, 2002.