In a study published in Cancer Research, women with a family history of breast cancer who worked with organic solvents prior to having their first child had an increased risk for hormone receptor-positive breast cancer.
"Our study is an important first step toward understanding how the timing of chemical exposures may impact breast cancer risk," says lead researcher Christine C. Ekenga, PhD, a postdoctoral fellow in the epidemiology branch of the National Institute of Environmental Health Sciences at the National Institutes of Health.
"We hope that our findings will generate additional interest in the possible role of solvents and other chemicals in the etiology of breast cancer."
This is not the first time exposure to solvents has been linked to increased cancer risk.
In 2004, a study published in the Proceedings of the National Academy of Sciences identified an industrial solvent that may put women at increased risk of breast cancers, miscarriages and irregular ovulation.
And in a 2013 study, researchers from the Danish Cancer Society Research Center in Denmark found an association between exposure to trichloroethylene - a widely-used chlorinated dry-cleaning solvent and degreaser - and increased risks of liver cancer and cervical cancer.
Data for the new analysis came from the 2003-2009 'Sister Study' cohort
Dr. Ekenga and her colleagues analyzed data from the Sister Study. This was a prospective cohort study involving 50,884 women who did not have cancer when the study began, but who were sisters of women who had been diagnosed with breast cancer.
Women who started working with solvents before their first full-term birth had a greater risk for breast cancer.
Covering the period 2003-2009, the Sister Study required participants to answer questionnaires about their employment history and a variety of other potential risk factors for breast cancer. The participants were also followed up for health updates on an annual basis.
Questions concerning solvent exposure were included as part of the study. The participants were quizzed on the duration of solvent exposure in their job, the weekly frequency of this exposure and the age they were during their first job involving organic solvents.
From this, the researchers behind the new analysis were able to include data from 47,661 of the total participants in the Sister Study.
Over the course of the study, 1,798 women were diagnosed with breast cancer. Of these women, 1,255 had invasive cancer, and 77% of these cancers were hormone-receptor positive.
The researchers adjusted the results for potential confounding from race/ethnicity, parity, exposure to tobacco smoke and whether or not the women worked night shifts.
Overall, they found no increased risk for breast cancer from exposure to solvents across the participants' lifetimes.
However, the researchers did find an association between solvent exposure prior to first full-term birth and increased risk for breast cancer. A "nonsignificant elevated risk" was observed in women who worked as maids or housekeeping cleaners and those who had jobs in factories.
Summarizing her findings, Dr. Ekenga says:
"The time between puberty and before first birth is an important period of development when the breast may be more vulnerable to chemical exposures. We observed that women who started working with solvents before their first full-term birth had a greater risk for breast cancer.
All women should be familiar with the chemicals and hazards that are present in their workplace, and use personal protective equipment and minimize exposures when appropriate."
Additional research is required to clarify the types of solvents - as well as the levels of exposure - that may present a risk to women in the workplace across different occupational settings.