A summary of the results from the Long Island Breast Cancer Study Project was published in the journal Nature Reviews Cancer in 2005.
"It might have hit pay dirt, but it didn't," says Deborah Winn, deputy director of the Division of Cancer Control and Population Sciences at the National Cancer Institute in Bethesda, Md., who wrote the review article. "It was terrific science, but no clear connection was found."
Similarly, Caucasian women in California's Marin County have historically had higher rates of breast cancer than their counterparts in surrounding urban counties, with 177 cases per 100,000 women in the years 1997 to 2001, according to data from the California Cancer Registry, a program of the state's public health department. That was 6% higher than the rate for the entire San Francisco Bay Area during that period, a difference that was statistically significant.
Studies on these women were smaller and used time spent in the county as a way to estimate exposure to environmental pollutants, but the bottom line was the same: no measurable contribution to breast cancer risk from environmental exposure. Factors that did correlate to disease included more frequent screening for breast cancer and consuming at least two alcoholic drinks per day. These results were summarized in a 2003 report in Breast Cancer Research.
Both regions are affluent communities, and higher socioeconomic status is associated with higher risk for being diagnosed with breast cancer. The reasons for this are not completely understood, but wealthier women tend to be older, have had fewer children and have their children later in life — all risk factors for breast cancer. They are also more likely to get mammograms on a regular basis, which increases the odds of finding any cancer that develops.
"In Long Island and Marin County, if you adjust for socioeconomic status, the high rates go away," Winn says.
The failure of these and other studies to make a link between pollutants and breast cancer has not convinced everyone that the two are unrelated. Many researchers and advocates are continuing the hunt.
Gray says her biggest concern is a class of chemicals called endocrine disrupters that includes bisphenol A (found in plastic bottles and the linings of metal food cans), phthalates (found in flexible plastic toys) and parabens (used as preservatives in many personal care products, such as shampoo and shaving cream).
"We're just now understanding that endocrine disrupters are particularly potent in the very young," she says, citing animal studies. Disrupting reproductive hormones during development seems to have long-term consequences, including susceptibility to tumor growth.
The National Cancer Institute and the National Institute of Environmental Health Sciences are collaborating on another large population study that aims to identify factors, including chemicals in the environment, that contribute to early puberty in girls, a known risk factor for breast cancer. Winn says it's a way of looking at one piece of the long trajectory from exposure to cancer. Results are expected soon, she says.
Meanwhile, many doctors want to keep the focus on undisputed risk factors that women can actually influence, such as their weight, diet, exercise routine and habits like smoking and drinking, Guth says. "These are things we can change — for the prevention of breast cancer and prevention of recurrence."