Breast augmentation: a risk factor for breast cancer?

BACKGROUND. A relation between breast augmentation and the subsequent risk of breast cancer has been postulated. Since an estimated 2 million women in the United States alone have received breast implants, even a small increase in the risk of breast cancer could have considerable public health consequences. METHODS. We performed a population-based nonconcurrent cohort-linkage study. All women in Alberta, Canada, who underwent cosmetic breast augmentation from 1973 through 1986 were included in the implant cohort (n = 11,676). This cohort was compared with the cohort of all women in Alberta in whom a first primary breast cancer was diagnosed (n = 13,557). The expected number of breast-cancer cases in the implant cohort was estimated by applying age-specific and calendar year--specific incidence rates of breast cancer (obtained from the Alberta Cancer Registry) to the implant cohort. Standardized incidence ratios were calculated by dividing the observed by the expected number of breast-cancer cases in the implant cohort. RESULTS. Forty-one patients with implants were subsequently found to have breast cancer. The expected number was 86.2. The standardized incidence ratio was thus 47.6 percent, significantly lower than expected (P less than 0.01). The average length of follow-up in the implant cohort was 10.2 years, and the average length of time from breast augmentation to the diagnosis of breast cancer was 7.5 years. CONCLUSIONS. Women who undergo breast augmentation with silicone implants have a lower risk of breast cancer than the general population. This finding suggests that these women are drawn from a population already at low risk and that the implants do not substantially increase the risk.