Breast cancer linked to chemical exposure

Study points to synthetic fibres, petroleum products

Vancouver Sun – April 1, 2010, p. B2

Exposure to certain chemicals and pollutants before a woman reaches her mid-30s could triple her risk of developing breast cancer after menopause, Canadian scientists said on Thursday.

In a study in Occupational and Environmental Medicine, a British Medical Journal title, the researchers found that women exposed to synthetic fibres and petroleum products during the course of their work appeared to be most at risk.

“Occupational exposure to acrylic and nylon fibres, and to polycyclic aromatic hydrocarbons may increase the risk of developing post-menopausal breast cancer,” they wrote.

But some experts commenting on the study expressed caution, saying such links can crop up by chance.

“In a study of this sort, positive associations often occur simply by chance,” said David Coggon, a professor of occupational and environmental medicine at Britain’s Southampton University. “They carry little weight in the absence of stronger supportive evidence from other research.”

The Canadian scientists conceded their findings could be due to chance, but also said they were consistent with the theory that breast tissue is more sensitive to harmful chemicals if the exposure occurs when breast cells are still active—in other words, before a woman reaches her 40s.

The researchers, from Montreal’s Occupational Health Research Institute based their findings on more than 1,100 women, 556 of whom were diagnosed with breast cancer in 1996 and 1997 when they were aged between 50 and 75 and had gone through the menopause.

A team of chemists and industrial hygienists investigated the women’s levels of exposure to around 300 different substances during their employment history.

After taking account of the usual factors associated with an increased risk of breast cancer, the analysis indicated a link between occupational exposure to several of these substances, the Montreal team wrote.

Compared with the comparison group, the risk peaked for exposures before the age of 36, and increased with each additional decade of exposure before this age, they found.

This meant women who were exposed to acrylic fibres appeared to run a seven-fold risk of breast cancer, while those exposed to nylon fibres almost doubled their risk.

The scientists said more detailed studies focusing on certain chemicals were now needed to try to establish what role chemical exposure plays in the development of breast cancer.

Reuters

The study Postmenopausal breast cancer and occupational exposures is authored by France Labrèche (Occupational Health, Quebec National Institute of Public Health, Montreal, Quebec, Canada, Départements de Médecine sociale et préventive et de Santé environnementale et santé au travail, Université de Montréal, Montreal, Quebec, Canada), Mark S Goldberg (Department of Medicine, McGill University, Montreal, Quebec, Canada), Marie-France Valois (Division of Clinical Epidemiology, McGill University Health Center, Montreal, Quebec, Canada) and Louise Nadon (INRS-Institut Armand-Frappier, Laval, Quebec, Canada) and can be found at Occup Environ Med 2010;67:263-269. The abstract is below.

Abstract
Objective To determine whether exposures in the workplace to organic solvents and to other agents, such as polycyclic aromatic hydrocarbons, are associated with increased risks of developing postmenopausal breast cancer.

Methods Between 1996 and 1997 a case–control study was conducted in Montreal, Quebec. Cases comprised 556 women, aged 50–75 years, with incident malignant breast cancer, and their controls were 613 women with other cancers, frequency matched for age, date of diagnosis and hospital. An expert team of chemists and industrial hygienists translated their job histories into exposure to about 300 agents.

Results Odds ratios (ORs) were increased for the usual risk factors for breast cancer and, adjusting for these, risks increased with occupational exposure to several agents, and were highest for exposures occurring before age 36 years. Increased ORs were found for each 10-year increment in duration of exposure, before age 36 years (OR<36), to acrylic fibres (OR<36=7.69) and to nylon fibres (OR<36=1.99). For oestrogen-positive and progesterone-negative tumours, the OR doubled or more for each 10-year increase in exposure to monoaromatic hydrocarbons, and to acrylic and rayon fibres. The OR<36 also doubled for exposure to organic solvents that metabolise into reactive oxygen species, and to acrylic fibres. A threefold increase was found for oestrogen- and progesterone-positive tumours, with exposure to polycyclic aromatic hydrocarbons from petroleum sources.

Conclusion Certain occupational exposures appear to increase the risk of developing postmenopausal breast cancer, although some findings might be due to chance or to undetected bias. Our findings are consistent with the hypothesis that breast tissue is more sensitive to adverse effects if exposure occurs when breast cells are still proliferating. More refined analyses, adjusting for hormonal receptor subtypes and studies focusing on certain chemical exposures are required to further our understanding of the role of chemicals in the development of breast cancer.

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