The widespread impression that breast implants increase the risk of developing breast cancer has little supportive evidence, according to a recent report in the Journal of the National Cancer Institute. Authors Louise A. Brinton and S. Lori Brown maintain that despite the well-documented diminution of ability to mammographically visualize lesions in women with implants, there are no definitive data confirming that disease prognosis is affected. Studies on the safety of silicone implants for breast cancer survivors should be encouraged, especially given that these devices can substantially contribute to the successful acceptance of a breast cancer diagnosis in many women.
Remarkably, a growing number of studies indicate that the risk of breast cancer may actually be reduced among women with implants. It is uncertain as yet the extent to which the reduction in risk might relate to methodologic limitations of the previous epidemiologic studies; mitigating factors include potential selection, surveillance, and reporting biases. In addition, because of the uncertainty of a biologic mechanism for the reduced risk, the purported reductions in breast cancer risk experienced by breast implant patients must be interpreted with caution.
The authors of the report observed that available data cannot yet confirm whether silicone implants predispose to other cancers. Experimental data, however, point toward the need for further evaluation of sarcomas and hematopoietic cancers, especially multiple myeloma and lymphomas.
Two descriptive studies have been undertaken to determine whether there have been changes in the incidence of sarcomas following the introduction of breast implants. No notable changes have been observed, although this methodologic approach would not be expected to have the power to detect associations unless exceedingly large effects were apparent. One investigation noted an increased prevalence of monoclonal gammopathies of undetermined significance among symptomatic women with implants, but results must be interpreted cautiously, given the referral nature of the study population.
Ongoing NCI Studies
The National Cancer Institute is currently conducting ongoing follow-up studies to determine the relationship of breast implants to subsequent cancer. It may be easier to resolve risks of cancer among women with silicone breast implants than those of other diseases believed to be caused by exposure to silicone implants, since reports of cancer can be validated against pathology reports, and cancer incidence rates in the general population are easily obtained.
Nevertheless, it will be essential for these studies to have adequate statistical power for evaluating cancer relationships and to consider other lifestyle factors that could independently affect disease risk. These studies must also take latency effects into consideration, particularly in light of the evidence of deterioration of the implant capsule over time and its possible association with immunologic changes. Studies focusing on women with long durations since initial implantation (eg, 10 or more years) that can account for the effects of explantation and reimplantation of different devices over time will therefore be necessary.
In conclusion, the authors noted that an issue left unanswered by most previous investigations is whether different types of implants have unique long-term effects. Of particular significance is whether there are any unusual effects of polyurethane foam-coated implants, given evidence that they can leak toluene diamine (TDA), a demonstrated carcinogen in animals. In one study, free TDA was detected in 80% of a group 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 1 in 1 million over the womans lifetime, which was considered to be a negligible risk.