Work exposure to weed killers tied to brain cancer

NEW YORK (Reuters Health) - Women whose jobs regularly expose them to weed killers may have a higher-than-normal risk of a particular form of brain cancer, results of a U.S. study suggest.

Researchers found that among more than 1,400 U.S. adults with and without brain cancer, there was no overall link between the disease and on-the-job exposure to pesticides or herbicides -- chemicals used to kill plants, usually weeds.

However, a closer look at the data showed that women who had ever been exposed to herbicides at work had a two-fold higher risk of meningioma than women with no such exposure.

Meningiomas are slow-growing tumors that arise in the tissue covering the brain and spinal cord. They are one of the most common forms of brain tumor, and occur most frequently in middle-aged women.

A few studies, but not all, have linked both farming and heavy pesticide exposure to a higher risk of brain cancer.

For the current study, published in the American Journal of Epidemiology, researchers looked not only at participants' job titles, but also at their estimated exposure to pesticides and herbicides.

They found that women exposed to herbicides had an elevated meningioma risk, and the risk tended to climb as the women's years of exposure increased. There was no link, however, been pesticide or herbicide exposure and brain cancer in men.

Unlike other forms of brain cancer, meningiomas are more common in women than men. The new findings suggest that herbicides might play some role in this risk, according to the investigators, led by Dr. Claudine M. Samanic of the National Cancer Institute in Bethesda, Maryland.

On the other hand, they write, the results are based on only a small number of women. In all, 33 women with brain cancer, and 71 without cancer, had ever been exposed to herbicides at work.

"Our finding that women exposed to herbicides experienced increased meningioma risk may be a chance finding, and our results should be interpreted cautiously," Samanic and her colleagues write.

Of the 17 women with the highest herbicide exposure, most worked in restaurants or grocery stores, and were likely exposed by routinely handling produce contaminated with herbicides, the researchers note.

It's not clear why pesticide exposure was unrelated to brain cancer in men or women. One possibility, the researchers note, is that only certain pesticides are involved in brain cancer risk, and they lacked information on which chemicals their study participants had used on the job.

And again, the researchers point out, only a small number of people had ever been exposed to pesticides at work, and the lack of a link to brain cancer could also be a "chance" finding.

SOURCE: American Journal of Epidemiology, April 15, 2008.