Certain PCBs Linked To Increased Risk Of Cancer

Colorectal cancer is the third most common human cancer, and the second leading cause of cancer-related death in Western countries, affecting men and women about equally. The causes of colorectal cancer are relatively poorly understood, although diet is thought to play an important role.

Diet is an important source of exposure to many synthetic organic chemicals used in industry and agriculture. Several of these, including PCBs, have been classified as probably or possibly carcinogenic to humans. PCBs were banned in 1976 in the United States. However, these highly toxic chemicals are very stable over time. They are widely present in the environment and are still considered a serious health threat.

In addition to considering the increased risk of colorectal cancer, the researchers looked specifically for mutation of two genes that might play a part in development of the disease. The risk associated with mono-ortho PCBs was slightly higher for tumors that also contained mutations of the p53 gene, but was not changed by mutations in the gene known as K-ras.

“Although colorectal cancer cannot be considered a hormone-dependent cancer, there is evidence that hormones play a role, at least in women,” the study authors write. “Studies of cancers of the pancreas and breast have shown that OCs [organochlorines] may interact with genetic alterations in tumors. Research on these interactions is relevant because they are frequent in colorectal cancer and one potential mechanism of OC toxicity may be the induction of mutations in these genes.”

Given the frequency of colorectal cancer, the findings should be considered further, according to Dr. Jim Burkhart, science editor for EHP. “The hypothesis in this paper certainly merits evaluation in further studies. It would also be helpful to know if other types of PCBs and other dioxins are found to impact the incidence of this disease,” he said.

The lead author of this study was Mike Howsam of the Laboratoire Universitaire de Medecine du Travail, in Lille, France. Other authors include Joan O. Grimalt, Elisabeth Guino, Matilde Navarro, Juan Marti-Rague, Miguel A. Peinado, Gabriel Capella, and Victor Moreno. The article is available free of charge at http://ehp.niehs.nih.gov/docs/2004/7143/abstract.html.

EHP is published by the National Institute of Environmental Health Sciences, part of the U.S. Department of Health and Human Services. EHP is an Open Access journal. More information is available online at http://www.ehponline.org/.