Researchers from the Silent Spring Institute search for clues to explain the higher incidence of breast cancer on Cape Cod.
The hypothesis that endocrine-disrupting chemicals affect the risk of breast cancer is a short, logical step away from what we already know about the disease. Since the 18th century, when the Italian physician Bernardino Ramazzini observed a higher incidence of breast cancer among nuns, researchers have known that women's natural reproductive hormones affect risk. More recently, Devra Davis with the World Resources Institute and her colleagues published the troubling hypothesis that other estrogenic compounds - including synthetic estrogens found in commercial products and the environment, as well as natural phytoestrogens in food - might also affect breast cancer risk.(1)
This hypothesis poses a critical challenge concerning the possible human health effects of endocrine disruptors, and, at the same time, it opens the doors for new research such as the Silent Spring Institute's study of breast cancer on Cape Cod. This research offers the hope of identifying preventable causes of the disease. Each year, 180,000 women are diagnosed with breast cancer in the United States. Preventable environmental factors - even if they represent relatively small, incremental risks - translate into many saved lives.
Multiple hormone-related mechanisms appear to be involved in breast cancer risk, and there are several ways that endocrine-disrupting chemicals may affect risk as well. Women who have never given birth - like the Italian nuns - and women who were older at the birth of their first child are at higher risk because the breast is not fully developed until after a first pregnancy, and the undifferentiated cells are more vulnerable to carcinogenesis. In addition, women with fewer children and those who were younger at menarche and older at menopause are at greater risk because each menstrual cycle results in exposure to estrogen - which causes cells to proliferate - increasing the chance of mutation and promoting growth of any existing tumor.
In addition, alcohol use, lack of physical exercise, higher body mass after menopause, and weight gain - factors that appear to increase estrogen levels - are associated with higher breast cancer risk, while removing the ovaries, the body's source of estrogen, before menopause, substantially reduces risk. Estrogen-based pharmaceuticals, including birth-control pills and hormone-replacement therapy, increase breast cancer risk, while treatment for breast cancer involves drugs such as tamoxifen that block estrogen.
Given the weight of evidence that endogenous and pharmaceutical estrogens affect breast cancer risk in multiple and complex ways, other hormonally active compounds in consumer products and the environment deserve careful study.
The seemingly simple question "Do endocrine-disrupting chemicals affect breast cancer risk?" does not lend itself to simple research methods, however. There is a large and growing list of compounds identified as endocrine disruptors. Their biological effects are diverse and as yet poorly understood, and scientists know little about how women are exposed or what aspects of exposure matter. Multiple research approaches are needed to disentangle the health effects of these compounds, and the challenge is particularly complex for diseases, like breast cancer, with long latency.
On Cape Cod, where breast cancer incidence is 20 percent higher than in the rest of Massachusetts, a multidisciplinary team, led by the Silent Spring Institute, is investigating the endocrine-disruptor hypothesis in the Cape Cod Breast Cancer and Environment Study. After three years of research, new methods and results are emerging that will inform studies of breast cancer and other hormonally mediated conditions.(2)
The Cape Cod Breast Cancer and Environment Study began in 1994 when the Massachusetts Department of Public Health published age-adjusted cancer-incidence rates by town. …