MIAMI BEACH, Fla--Six studies of women with silicone breast implants and no personal history of breast cancer have all found a relative risk of breast cancer of less than 1.0 (range, .24 to .67).
"If the relative risk is less than 1, you actually have fewer cancers in the implant group than in the control group," Kenneth A. Kern, MD, said at the 12th Annual International Breast Cancer Conference.
There is no causal relationship between silicone breast implants and cancer, he said: "They don't cause breast cancer, and they don't cause sarcomas. I don't think they're protective, but we're not sure why the relative risk is less than 1. It may have something to do with the old theory of 'less breast, less breast cancer.'"
Dr. Kern, attending surgeon, Hartford Hospital, and associate clinical professor of surgery, University of Connecticut School of Medicine, Farmington, described silicone as a manufactured, stable, long-chain compound constructed from the atom silicon. "It is not a crystal like silica, which causes asbestosis," he emphasized.
He also noted that studies linking implanted foreign bodies in rodents with development of sarcoma are unique to rodents: "This effect has never been seen in an animal phylogenetically higher than a rat."
The polyurethane used to coat silicone implants contains single molecule fragments that, if given in huge amounts, have been shown to cause tumors in rodents, Dr. Kern said. One of those fragments, toluene diamine, has been classified as a class B carcinogen, which, by definition, means it has never been known to produce a tumor in a human. "Saccharin, estrogen, and progesterone(Drug information on progesterone) are also class B carcinogens," he said.
Dr. Kern and his colleagues studied this issue using data from 35 Connecticut hospitals. They correlated discharge codes for silicone breast implants from 1980 to 1994 with information from the Connecticut tumor registry.