Studies Show No Increased Breast Ca Risk in Women With Silicone Implants

MIAMI BEACH, Fla--Six studies of women with silicone breast implantsand no personal history of breast cancer have all found a relativerisk of breast cancer of less than 1.0 (range, .24 to .67).

"If the relative risk is less than 1, you actually have fewercancers in the implant group than in the control group,"Kenneth A. Kern, MD, said at the 12th Annual International BreastCancer Conference.

There is no causal relationship between silicone breast implantsand cancer, he said: "They don't cause breast cancer, andthey don't cause sarcomas. I don't think they're protective, butwe're not sure why the relative risk is less than 1. It may havesomething to do with the old theory of 'less breast, less breastcancer.'"

Dr. Kern, attending surgeon, Hartford Hospital, and associateclinical professor of surgery, University of Connecticut Schoolof 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 inrodents with development of sarcoma are unique to rodents: "Thiseffect has never been seen in an animal phylogenetically higherthan a rat."

The polyurethane used to coat silicone implants contains singlemolecule fragments that, if given in huge amounts, have been shownto 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 producea tumor in a human. "Saccharin, estrogen, and progesteroneare also class B carcinogens," he said.

Dr. Kern and his colleagues studied this issue using data from35 Connecticut hospitals. They correlated discharge codes forsilicone breast implants from 1980 to 1994 with information fromthe Connecticut tumor registry.

The computer search found 680 patients with silicone breast implants,all of whom had at least one year of follow-up. One year was chosen,he said because "many of the law suits have been in patientswho developed cancer very soon after an implant was placed."The average follow-up in the study was about 6 years.

The control population consisted of 1,022 women undergoing tuballigation between 1981 and 1985.

The results showed no statistical difference in the rate of breastcancer between the two groups: four breast cancers were foundin the implant group (0.59%) and nine in the control group (0.88%),for a relative risk of .67 in the implant patients.

Non-breast cancer tumors in the implant group included two lungcancers, one rectal cancer, and one eyelid cancer. "Therewere no sarcomas," he said. The control group had significantlymore non-breast cancer tumors, primarily gynecologic cancers,which may be explained by the close surveillance of the controls,who were undergoing sterilization.