Part of the National Cancer Institute Breast Implant Study
Authors: Louise A. Brinton, Jay H. Lubin, Mary Cay Burich, Theodore Colton, S. Lori Brown, and Robert N. Hoover.
In 1992, because of the lack of sufficient evidence on the long-term safety of silicone gel breast implants, Congress directed the National Institutes of Health (NIH) to undertake a large follow-up study to evaluate the health effects of the implants. The National Cancer Institute (NCI) subsequently conducted one of the largest studies on the long-term health effects of silicone breast implants. The purpose of the NCI study was to evaluate the effect of breast implants on the risk of developing breast cancer, developing some cancer (other than breast cancer), developing connective tissue disorders, and dying (from all causes).
To ensure scientific objectivity the study was designed and funded entirely by the government. Scientific oversight was provided by NCI’s Board of Scientific Counselors and its Breast Implant Study Advisory Panel, a multidisciplinary panel of academic scientists, including oncologists, plastic surgeons, rheumatologists, and epidemiologists, as well as patient advocates and consumer representatives.
NCI Study Design
This retrospective cohort study included 13,488 women who had breast implant surgery (in both breasts) for cosmetic reasons between 1962 and 1989; 3936 women of similar age who had some other type of facial or abdominal plastic surgery were selected as the control group. Both groups of women were selected from 18 plastic surgery practices that had performed large numbers of cosmetic breast augmentation surgeries, in the geographic areas of: Atlanta, Ga.; Birmingham, Ala.; Charlotte, N.C.; Miami and Orlando, Fla.; and Washington, D.C.
The NCI study reviewed the women’s medical records and collected information about the surgical procedure, the type of breast implant they received, any complications that occurred, and factors which might affect health status (such as body weight and medical history).
Patients who were located were asked to complete a questionnaire (sent by mail) to collect additional information. The questionnaire asked whether they had subsequent plastic surgery, inquired about lifestyle factors that could affect their health (menstrual, pregnancy, and breast-feeding history, body weight, hormone use, alcohol consumption, cigarette smoking, and other medical problems), and included extensive follow-up on potential short-term complications (rupture) and longer-term complications (diagnosis of cancer, or any symptoms or diagnosis of connective tissue diseases).
Physical exams were not performed on the patients, but attempts were made to confirm the (information gathered through the questionnaire about) patient reports of cancer and connective tissue disease by further reviewing the medical records of the oncologists, rheumatologists, and other physicians who diagnosed and/or treated these diseases.
For patients who had died, death certificates were collected to verify the causes of death.
About 80% of the original 13,500 implant patients and 4,000 patient controls were successfully located; and about 70% of those women completed the questionnaires. These percentages are similar to other comparably designed epidemiologic studies.
Among the women with breast implants, 49.7% received silicone gel implants, 34.1% received double lumen implants, 12.2% received saline-filled implants, 0.1% received other types of implants, and 3.8% received an unspecified type of breast implant.
Importance of the NCI Study
Important features of this study included the large number of women evaluated, the control group used, the detailed and extensive collection of information, and the length of follow-up.Never before had a study about silicone gel breast implants included so many women.
- Never before had a study about silicone gel breast implants included so many women.
- An important and unique feature of the NCI study is that the breast implant patients were compared to women in the general population, and to women who had received other types of plastic surgery. In studies published previously, the general population had been used as the control group. However, NCI investigators learned in an earlier study(1) that women with breast implants tend to share more breast cancer risk factors with women who had received other types of plastic surgery, than with the general population. These risk factors include a history of previous operations for benign breast disease and/or gynecologic problems. The NCI researchers therefore believed that women who received other types of plastic surgery may be a more appropriate comparison group than the general population.
- The NCI study was more comprehensive in its evaluation because it included more detailed information about the types of breast implants and numerous risk factors affecting health, [such as the patient’s medical history, screening medical practices (mammograms, colonoscopy, Pap smear, HPV test), and lifestyle behaviors] that were not included in previously published reports.
- The average length of follow-up was 12.9 years among the implant patients and 11.6 years among the comparison patients. This was longer than in previously published studies where women with breast implants had been followed for less than 10 years.
NCI Study results
The first part of the NCI’s analysis of the health risks of breasts implants evaluated the effect of breast implants on the risk of developing breast cancer. The results were published in the October 2000 issue of Cancer Causes and Control [Vol.11(9):819-827].
- The NCI study found no association between breast implants and the subsequent risk of breast cancer.
- This study evaluation spanned 26 years (1962-1988), during which time many changes took place in breast implant design and manufacturing. Despite changes in gel composition, implant shell thickness, and the introduction of shell barrier coatings the risk of breast cancer did not change with any of the types of implants.
- Some controversy existed about whether women with breast implants had more advanced breast cancer at the time of diagnosis, when compared to women without implants. The NCI study did demonstrate that women with breast implants did have a smaller percentage of in situ (localized, non-invasive, early stage) breast cancer and a somewhat later stage of cancer at the time of diagnosis. But, the differences were not statistically significant, and there was no significant difference in breast cancer mortality between the implant and control group.
- Prior epidemiologic studies had generally shown women with breast implants to have a reduced risk for breast cancer. For women followed for more than 10 years, the NCI study showed there was no change in breast cancer risk; it therefore failed to confirm that exposure to breast implants reduces a woman’s risk for breast cancer.
- At the time of this study, about 80% of breast implants in the US were for cosmetic reasons, and about 20% were for breast reconstruction. This study did not evaluate women undergoing breast reconstruction after breast cancer surgery. The NCI study does not draw any conclusions about the health risks of breast implants on patients diagnosed with breast cancer.
The NCI would perform further analysis of the data to evaluate the risk of other cancers, connective tissue disorders, and causes of death. Their findings were published in other reports between 2001 and 2006.
(1) Brinton, Louise et. al., Characteristics of a Population of Women with Breast Implants Compared with Women Seeking Other Types of Plastic Surgery, Plastic and Reconstructive Surgery 2000; 105(3):919-927.