A recent study conducted by scientists at the National Institute of Environmental Science found that women who work with organic solvents had a greater risk for developing breast cancer. Researchers used data on women taking part in the Sister Study, which has followed more than 50,000 women whose sisters had breast cancer. Lead authors, Christine Ekenga and Dale Sandler, answered our questions about the meaning and significance of the study.
What are organic solvents and why should we care about them?
Organic solvents are chemicals that are used to dissolve other compounds. Some of the health hazards associated with solvent exposure include respiratory irritation, reproductive damage, heart damage, and liver and kidney damage. Solvents have also been associated with some cancers. Health effects are more likely to occur with higher levels of exposure. The health effects of low level exposures (one time or over a long time period) are less well established.
Millions of workers are exposed to organic solvents on a daily basis. What kinds of jobs expose people to them?
Solvents are found in a variety of products, such as cleaning products, degreasers, detergents, paint thinners and dry cleaning solutions. For example, women who work as clinical laboratory technicians, maids, and factory workers, may be exposed to organic solvents on the job.
Could you explain the methods used in this study?
The Sister Study is a long-term study of more than 50,000 women who have had a sister with breast cancer. When the study began, none of the participants had been diagnosed with breast cancer. At enrollment, we collected information about their lifestyle, reproductive history, and work history, including solvent exposure at different time periods. For this analysis, we analyzed data from approximately 47,000 women who provided detailed work histories. Our analysis was designed to identify associations between solvent exposure before they entered the study and the development of breast cancer afterward.
What did your study find specifically?
We observed that women who started working with solvents before their first full-term birth had a greater risk for breast cancer.
Are there other studies that demonstrate a link between organic solvents and breast cancer?
Yes. Solvents have been shown to cause breast tumors in animals.
There’s a difference in risk for women who have had children and those who have not. Could you explain that?
We know that the time period between puberty and before first birth is an important period of development when the breast may be more vulnerable to chemical exposures. We also know the breast undergoes changes during pregnancy. Our findings support the hypothesis that chemical exposure during a vulnerable period of breast development may increase the risk of breast cancer in women.
What first attracted you to this area of research and what spurred this specific study?
Few studies have looked at occupational exposures in women. What is unique about the Sister Study is that we have collected a large amount of information about occupational and environmental exposures from more than 50,000 women. Because solvents have been shown to cause breast tumors in animals, we were interested in looking at the relationship between solvents and breast cancer in humans.
Tell me about the Sister Study- why is this study important?
The Sister Study is a long-term study of more than 50,000 women who have had a sister with breast cancer. The women come from all over the country and Puerto Rico, from all walks of life. Its goal is to examine the impact of environmental and occupational factors on breast cancer risk. When we began the study, many other large breast cancer studies were already in progress, but most of them focused on dietary, lifestyle, and reproductive factors. We wanted to not only concentrate on associations between environment and breast cancer risk, but also study the combined effects of genetic and environmental factors that may increase the chances of getting breast cancer.
Sisters of women with breast cancer have about twice the risk of developing breast cancer as other women, so by studying large numbers of them for at least 10 years, the Sister Study is much more powerful than other breast cancer studies.
How does this study differ or compare with the Brophy study?
The Brophy paper examined breast cancer risk associated with endocrine disruptor chemicals in the workplace. While both studies identified several occupations in which solvent exposure was associated with an elevated risk of breast cancer, including production occupations, there are several differences.
The Brophy paper examined endocrine disrupting chemicals as a group, while our study focused on solvents. The Brophy study was a case-control study, which compared women with breast cancer to a control group of women without breast cancer. In contrast, the Sister Study was a prospective cohort study, which means we collected exposure information before the women were diagnosed with breast cancer. Brophy and colleagues used experts to classify jobs based on how likely they were to include the use of specific chemicals, while we relied on what women told us about their use of solvents on the job. Despite these differences, both studies are important first steps toward understanding the relationship between work-related chemical exposures and breast cancer in women.
Dale P. Sandler, Ph.D is a senior investigator and Branch Chief of the Epidemiology branch at the National Institute of Environmental Health Sciences (NIEHS). She is Principal Investigator of the Sister Study and other large prospective cohort studies, including studies of pesticide applicators and their families and persons who helped clean up after the 2010 Deepwater Horizon oil spill in the Gulf of Mexico.
Christine C. Ekenga, Ph.D. is a Postdoctoral Fellow in the Epidemiology Branch at NIEHS. At NIEHS she studies risk factors for breast cancer and health effects of the Gulf of Mexico oil spill.