It is unfortunate that the media has given the impression that few environmental factors have been associated with human cancer. The World Health Organization's International Agency for Research on Cancer has identified 80 natural and synthetic chemicals, occupational situations and viruses that cause cancer in humans. We do not have exposure data or cancer risk data for the tens of thousands of chemicals that are in common use in the home and workplace. The National Toxicology Program has successfully used screening tests in rodents to identify potential human carcinogens, including those chemicals that cause mammary (breast) tumors. Of the 509 compounds evaluated, nearly 9% (42) have been identified as causing breast tumors in laboratory rodents. The types of chemicals are diverse and include industrial chemicals, dyes, flame retardants, solvents, pesticides, toxins from molds, and pharmaceuticals.
The American Cancer Society predicts that over 205,000 new cases of breast cancer will be diagnosed in Americans, and 40,000 will die of the disease in 2002. We do not have a complete picture of the biology of the disease nor of the many factors that affect its risk. The complexity of breast cancer dictates that it is not possible for one study to provide all the data needed to fully identify its causes. It is not possible to paint the picture of breast cancer in a single stroke. Rather, each study contributes a small piece to a mosaic of breast cancer risk.
The hypothesis of whether blood levels of organochlorine pesticides (such as DDT, chlordane or dieldrin) or certain industrial contaminants (such as polychlorinated biphenyls) predict breast cancer risk has been tested in over 30 studies, most recently in the Long Island Breast Cancer Project (LIBCP). Most studies of white Western adult women have not shown that blood or fat levels of these compounds predict breast cancer risk. It is still unclear whether women of other ethnic backgrounds may have a higher breast cancer risk from past or current DDT exposure, or whether exposure during early periods of breast development affects later risk. Whether past exposures to organochlorine chemicals affects the aggressiveness of breast cancer needs to be explored more fully. For other chemicals, including polyaromatic hydrocarbons, the LIBCP study results suggested a modest increased breast cancer risk associated with exposure to these compounds, which are found in charred foods, cigarette smoke and burned fossil fuels.
The LIBCP needs to be embraced as an evaluation of important hypotheses. Because selected chemicals were not associated with breast cancer risk this should not result in abandoning all research on how environmental factors affect the risk of this complex disease. It should force us to refocus our thinking, our approach, and refine the tools and methods needed to test future hypotheses.
For example, the timing of exposure to environmental factors affects future breast cancer risk. Japanese infants and girls exposed to ionizing radiation at Nagasaki and Hiroshima subsequently had a very high breast cancer risk compared to women who were over 40 when exposed. Recent research suggests high exposure to the environmental contaminant dioxin in younger women may increase breast cancer risk later in life. Silent Spring Institute researchers are characterizing household exposures to environmental toxins in women with and without breast cancer on Cape Cod. The "Agricultural Health Study" is evaluating whether exposure to agricultural chemicals affects health, including cancer risk, in over 85,000 men and women in farm families from North Carolina and Iowa. The "Sister Study" will follow over 50,000 sisters of women with breast cancer in an attempt to identify causes, including possible environmental links, to the disease. The results from these studies will better inform regulatory agencies, and at risk populations of the environmental factors that do and do not pose a cancer risk in target populations.
Much media attention has focused on the role cancer activists and policy makers play in influencing funding for cancer research. The Roswell Park Cancer Institute had its modest beginning over 100 years ago because of the persistent efforts "on the part of a number of men, both professional and laymen, both in and out of the Legislature" who influenced the New York legislature to appropriate "a small sum for the purpose of equipping and maintaining a laboratory devoted to this kind of [cancer] research" (quote from Dr. Roswell Park, Transactions of the Medical Society of the State of New York,1899).
A series of workshops were held this past year at the National Institute of Environmental Health Sciences. Scientists, risk assessors and cancer activists engaged each other in a full discussion of approaches that could be used to better evaluate and understand the role of environmental factors in breast cancer risk. Such interaction and partnerships are not only necessary, they are instrumental in enabling us to foster research agendas that will ultimately lead to risk reduction strategies for ourselves and our children.
This article can also be found at: http://envirocancer.cornell.edu/Newsletter/articles/v7where.cfm
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