Breast implant and cancer Polyurethane Foam Covered Breast Implants >>
The relationship of polyurethane foam-covered implants to cancer risk bears special attention.
These devices have been estimated to account for approximately 10% of all implanted silicone implants. Originally designed to decrease the risk of breast contracture, polyurethane implants were withdrawn from the market in 1991 when the FDA found that the polyurethane could degrade into 2,4- and 2,6-toluene-diisocyanate diamines (TDAs) (104). TDAs have been shown to cause cancer in laboratory animals (mice: cancers of the liver, ovaries, spleen, subcutaneous tissue, and peritoneum; rats: cancers of the pancreas and liver and breast fibrosarcomas) and are recognized as animal carcinogens (105). There is evidence of increased cancer rates when 2,4-TDA is injected subcutaneously (106), painted on the skin (107), or added to the diet (108,109), and a statistically significant dose-response relationship between ingestion of 2,4-TDA and breast cancer in rats has been shown (108). High rates of cancer have been found in rodents at the injection site and in the liver, lung, and breast (104). Although these studies suggest that breakdown products may be human carcinogens, it must be noted that the dose from polyurethane implants is much lower than that used in these animal studies. Data on human consequences of polyurethane implants are limited to a follow-up study of 213 patients, whose exposure ranged from 1 year to 18 years (110). Two patients developed breast adenocarcinomas, of questionable relevance given the absence of any comparison group.
Additional concern regarding the carcinogenic potential of TDA derives from the chemical being found in the urine of a patient several months following insertion of a polyurethane breast implant (111). These breakdown products have also been found in the urine and plasma of subjects experimentally exposed to toluene diisocyanate and in workers in the polyurethane-manufacturing industry (112). Two cohort studies (113,114) of cancer risk among individuals occupationally exposed to diisocyanates in the production of polyurethane foam noted some excesses of cancers of the pancreas, rectum, and lung and of non-Hodgkin's lymphoma, despite overall cancer risks that were below unity. Both studies, however, were limited by the numbers of observed cancers and by an inability to control for extraneous factors, such as cigarette smoking.
Because of the uncertainty of the risk for humans, the manufacturer of polyurethane foam-covered implants suspended sales of these implants and performed a study to measure TDA levels in body fluids of women with the implants. Free TDA was detected in the urine of 80% of 61 women with the implants, compared with 13% of 61 women without the implants. On the basis of this information, the FDA estimated the risk of cancer from exposure to TDA from this type of implant to be about one in one million over the woman's lifetime, which was considered to be a negligible risk (115,116).