The paper (J Natl Cancer Inst 2006;98:557-559) reports outcomes in a nine-year extension of an earlier nationwide cohort study. It followed 3,486 breast implant recipients for a mean of 18.4 years (range 0.1 to 37.8 years) and included an additional 28,627 person-years of follow-up and 106 additional cancers compared with the initial report.
Statistical comparisonsStatistical comparisons of incidence rates of cancer in the study cohort and among women in the general population were performed by calculating standardized incidence ratios and 95 percent confidence intervals.
The results showed there were no significant differences between the two groups in rates of cancer overall or for almost all other site-specific cancers, including brain cancer, sarcoma, non-Hodgkin lymphoma and multiple myeloma — malignancies for which possible safety concerns have been raised by other studies.
Also noteworthy, the study found women with breast implants had a statistically significant, 30 percent lower incidence of breast cancer relative to the general population.
"This is the longest study of cancer incidence among breast implant patients published to date," says Joseph K. McLaughlin, Ph.D., lead author of the study and president, International Epidemiology Institute, Rockville, Md.
"With average follow-up now reaching almost 19 years and two-thirds of the women with breast implants followed for at least 15 years, it is remarkable that we continued to find no evidence of an excess risk of cancer related to the implant itself. Given the duration of our study and the other strengths of its design, we believe our findings provide the closing chapter to this story," Dr. McLaughlin says.
Lung cancer up
Only lung cancer was found to occur at a significantly increased incidence among the cosmetic breast implant recipients. However, that result can be explained by a higher rate of smoking among the cosmetic breast implant patients compared with the general population, Dr. McLaughlin says.
"We previously interviewed a subset of these women and found they were nearly three times more likely to be current smokers compared with the general population," he notes.
Dr. McLaughlin also points out that the reduced incidence of breast cancer is not attributable to the cosmetic implants but rather is the result of other intrinsic characteristics of the cosmetic implant patient population.
"Compared with the general population, women who undergo augmentation mammoplasty tend to be younger at first birth and have a higher parity and lower body mass index. Those features are all associated with a reduced risk of breast cancer.
"In addition, they may represent a selected population of women that excludes individuals diagnosed with breast cancer during preoperative screening, as well as those with a family history of breast cancer," he explains.
Dr. McLaughlin observes that the Swedish setting for the nationwide, population-based study is one of its key features because of the opportunity to collect nearly complete data on cancer development in that country. Sweden has nationwide population and healthcare registries, as well as a personal identification system enabling record linkage with minimal losses to follow-up.
The investigators used the Swedish Inpatient Register to identify women who underwent cosmetic breast implantation between January 1, 1965 and December 31, 1993, and linkage to the Cancer, Death and Migration Registers to identify incident cancer cases recorded through December, 2002. Cancer diagnosis was determined from the Swedish Cancer Register that has been shown to be a reliable and complete source for case ascertainment.
"There are few if any weaknesses to our study design, and we believe it certainly provides more accurate data than could be obtained in a study performed in the U.S.," Dr. McLaughlin says.
CST POINT Dr. McLaughlin also points out that the reduced incidence of breast cancer is not attributable to the cosmetic implants but rather is the result of other intrinsic characteristics of the cosmetic implant patient population.