Carcinogenic potential of silicone breast implants: a Connecticut statewide study

To clarify the carcinogenic potential of silicone breast implants, 680 implant procedures performed on women in Connecticut with no prior history of cancer were correlated with the subsequent development of primary breast and nonbreast cancers. Neoplastic events after the placement of silicone breast implants during the 13-year interval from October 1, 1980, through September 30, 1993, were quantified using a retrospective, linked-registry method. ICD-9-CM discharge codes contained in the Uni formed Hospital Discharge Data Sets (UHDDS) from 34 hospitals across Connecticut were linked to procedure codes for unilateral and bilateral implants, and to medical histories for new malignancies after the implant procedures. Data were cross-linked to the Connecticut Tumor Registry to confirm the clinical history of each cancer. The rates of breast and nonbreast cancers in patients with silicone breast implants were compared with those of a control population drawn from the UHDDS of 1022 women undergoing sterilization by tubal ligation between 1981 to 1985. Ages (mean +/- SD) were similar in the implant group (34 +/- 10 years) and in the sterilization group (32 +/- 6 years). The mean follow-up in the implant group (4.6 years) was also similar to that of the control group (5.4 years). Compared with the control group, the implant group demonstrated lower rates of breast cancer (0.59 versus 0.88 percent, p = 0.35) and nonbreast cancer (0.59 versus 2.7 percent, p = 0.001). Correspondingly, the implant group had a lower relative risk of breast cancer (relative risk = 0.67, 95 percent, confidence interval = 0.20 to 2.17) and nonbreast cancer (relative risk = 0.21, 95 percent, confidence interval = 0.07 to 0.60). Based on these data, it was concluded that silicone breast implants are not carcinogenic, because they are not associated with increased rates of either breast or nonbreast cancers. The validity and threats to the conclusions are discussed, and the results are placed into context with similar findings from other studies.