In the early 1970s, Amy Present shared a house with friends in Newton, Massachusetts. Of the seven women who lived there, four were later diagnosed with cancer—including Present, who was treated for breast cancer in 1984. The other three women died. Two decades later, Present learned that she had been living in a neighborhood whose breast cancer incidence is 37 percent higher than the state average.
Between 1982 and 1992, the city of Newton, Massachusetts, had a breast cancer rate that was 11 percent higher than that of the state as a whole. The breast cancer rates are uneven within the city, ranging from 22 percent below to 55 percent above the state average.
With funding from the Massachusetts Department of Public Health, Silent Spring launched a study into the factors that may have contributed to those elevated breast cancer rates. The study involved approximately 1,350 Newton women who responded to a questionnaire about their health history, individual characteristics, habits, and home environments.
Traditional individual characteristics known to affect breast cancer risk, including reproductive history and family history of breast cancer, accounted for only 5 percent of the difference in breast cancer rates between high- and low-incidence areas. Possible environmental risk factors, which are associated with higher income and education, contribute 14 percent to the difference between high- and low-incidence areas. Possible environmental factors include use of lawn services, dry cleaning, and pesticide use.
At the outset of the study, census data showed that residents of Newton’s higher incidence area had higher incomes than those in the low-incidence neighborhood. Survey results similarly showed higher income, education, and other indicators of higher socioeconomic status in high-incidence areas.
Because income and education are not themselves causes of breast cancer, further analysis investigated whether the well-known association between socioeconomic status and breast cancer risk may have been the result of environmental exposures. Results showed that significantly greater use of certain products among higher socioeconomic status women contributed to differences between high- and low-incidence areas:
- 65 percent of women in high-incidence areas reported using professional lawn services, compared with 36 percent in low-incidence areas.
- 17 percent of women in high-incidence areas reported using termite treatments in their homes, compared with 9 percent in the low-incidence areas.
- 30 percent of women in high-incidence areas reported high routine use of pesticides, compared with 23 percent in low-incidence areas.
- 36 percent of women in high incidence areas reported use of flea and tick products, compared with 42 percent in low-incidence areas, a pattern in contrast to results on use of other chemical products.
The researchers found these findings intriguing because many pesticides contain endocrine disrupting compounds (EDCs) that mimic our natural hormones. Exposure to EDCs is an emerging area of study for breast cancer risk. Since a woman’s lifetime exposure to natural estrogen is linked to higher breast cancer risk, exposure to compounds that mimic estrogen and other hormones may also increase risk.
Higher rates of mammography and breast self-examination in high-incidence areas are likely to contribute to higher reported breast cancer rates: 27 percent of women in high-incidence areas said they had had at least 10 mammograms, compared with 17 percent in low-incidence areas. Because screening leads to earlier diagnoses, it may contribute to temporarily higher reported incidence.
The higher proportion of Jewish women in high-incidence areas did not account for the difference in incidence between the study areas.
The study team included researchers from JSI Research and Training Institute, Inc. and Applied Geographics, Inc.