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
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
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 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
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.