US breast cancer study suggests risks from chemicals

BMJ 1994; 308 doi: (Published 23 April 1994) Cite this as: BMJ 1994;308:1057
  1. F B Charatan

    A study by the New York State department of health suggests that post- menopausal women who lived near a chemical plant on Long Island between 1965 and 1985 were at increased risk of breast cancer. The study found that the risk for women living within one square kilometer of a chemical plant during that time was 60% greater than for women who lived elsewhere. This calculation took into account other known risk factors for the disease.

    Breast cancer support groups on Long Island have campaigned for years for research into environmental causes of the disease. The rate of breast cancer among women is 112 per 100 000 in Nassau County and 107 in Suffolk County - well above the statewide average rate of 96 per 100 000. The two year study involved 1759 women who had lived on Long Island for at least 20 consecutive years prior to 1985. Using geographic computer software, Long Island was divided into 5809 grid cells of one square kilometer to study proximity to industrial plant. All known addresses for women in the study were located within these grids and weighted for length of residence.

    Researchers examined the records of 793 women in whom breast cancer was diagnosed between 1984 and 1986 and compared them with a control group of 966 Long Island women selected from motor vehicle records during the same period who did not have breast cancer. The results were similar in both Long Island counties, but did not reach statistical significance in Suffolk County, possibly because of fewer study participants living there and less industry, particularly in 1965. No association was found between breast cancer risk and traffic volume. The study also showed no increased risk for breast cancer in premenopausal women.

    The increased risk identified in the study appeared to be greater 30 years ago than it was 20 years ago. Health officials speculate that more stringent air pollution standards established over the past 30 years could have been a factor in the decreased risk. Also, risk increased with the number of chemical plants located near the women's homes. Dr Roger Grimson, a biostatistician and associate professor of preventive medicine at the State University of New York at Stony Brook, said that the study showed a small, weak association between women with breast cancer, and residence near a chemical plant on Long Island. There were no specific exposure measurements, and there were some biases in the selection for the sample studied. He said, “The study probably pushed that type of data as far as it could go.”

    New York State Health commissioner Dr Mark Chassin said, “It is important to understand that no cause and effect relationship is demonstrated by our study. We have found a statistical association which demands further investigation. We have no data at this point that directly link any specific industrial site or substance with breast cancer risk.” Dr Chassin said that his agency will undertake further analyses in cooperation with the state department of environmental conservation, and will also work with the National Cancer Institute in its agenda on breast cancer research for Long Island.

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