Answer:
Animal experiments have demonstrated a decreased incidence of breast cancer in rats who received silicone implants before stimulation with a proven carcinogen. Animals implanted with silicone breast prostheses beneath the mammary tissues had a statistically lower incidence of breast cancer than control subjects by a margin of 52.5%. The authors concluded that silicone does not increase the risk of carcinoma, but may actually decrease it by exerting a local effect on mammary tissues. Animals with dorsal implants situated away from mammary tissues had a 34% higher incidence of carcinoma than those with submammary placement. The hypothetical protective effect noted in that study appears to be related to local contact at the mammary tissue level and macrophage activation following capsule formation. In another report with similar findings, blood from women with breast implants killed breast cancer cells in tissue culture.
Two large epidemiologic studies have examined the subsequent risk of breast cancer following augmentation, one based on an implant cohort of 11,676 women in Alberta, Canada, who were followed for 13 years, and a second study in Los Angeles with patients who have had a median of 15.5 years of silicone implant exposure. These studies concluded that a lower incidence of breast carcinoma was found in augmented patients than in nonimplanted control subjects. It is noteworthy that women in the Alberta study did not have polyurethane-coated implants. Some possible explanations for these unexpected findings are that smaller-breasted women may be less predisposed to get breast cancer, or perhaps silicone mediates a biologically protective effect against breast cancer.