Silicone implants and the inhibition of cancer.

The safety of augmentation mammaplasty and its relationship to breast cancer has been a much debated topic. The authors previously showed a decreased incidence of breast cancer in rats who had received silicone implants 2 weeks before carcinogen stimulation. The present study was designed to determine (1) whether this protective effect is influenced by the location of the implant, and (2) whether tumor incidence could also be altered in spontaneous mammary tumor-forming animals, the C3H/OuJ mice. (1) A total of 110 rats received either a silicone implant or a sham operation in one of three locations: inframammary region, dorsum, or intraperitoneal cavity. Methylnitrosoured (MNU) injections occurred 14 days after implantation. Animals were examined weekly for tumor growth and were killed 250 days after MNU injection. Animals with silicone implants beneath the mammary gland had a statistically significant lower incidence of breast cancer formation (11.5 percent) compared with both dorsally implanted animals (45.8 percent) and sham controls (64 percent). (2) Sixty C3H/OuJ mice underwent implantation of either a silicone implant, free silicone gel, silicone sheet, or a sham operation. At 50 weeks of age, after weekly examinations, the animals were killed. The cancer incidence in mice with silicone implants was 17 percent compared with 50 percent found in sham controls. Exposure to a silicone prosthesis at an early age does not seem to increase tumor incidence and may even have a locally protective effect against breast cancer formation.