Silicone breast implant study and breast cancer risk: questions and answers

1. What is the purpose of the breast implant study?

The National Cancer Institute (NCI) is conducting a study to determine the long-term health effects associated with silicone breast implants, including any changes in breast cancer risk. Although implants have been linked to various short-term complications, less is known about their long-range effects. The current study, evaluating breast cancer risk and breast implants, appears in the November issue of Cancer Causes and Control.

Future analyses will evaluate the occurrence of other cancers and connective tissue disorders, as well as the causes of death. The characteristics of the 13,500 participants and 4,000 comparison patients in the study are described in a paper published in March 2000 (see question 7).

2. Why was the study initiated?

Breast implants were first marketed in the early 1960s, before the 1976 Medical Device Amendments to the Food, Drug and Cosmetic Act required that medical devices be shown to be safe and effective. Silicone was initially assumed by manufacturers to be biologically inactive and, therefore, to have no harmful effects. However, cases of connective tissue disorders and cancers were reported in several short-term studies.

Because there were few reports on the long-term safety of implants, in 1992, the Food and Drug Administration (FDA) restricted the use of silicone gel breast implants to controlled clinical trials of women seeking breast reconstruction. To address many of the unanswered questions, Congress directed the National Institutes of Health in the same year to undertake a large follow-up study to assess the long-term health effects of exposure to silicone breast implants.

It is estimated that between 1.5 and two million women in this country have had breast implants since they first appeared on the market. Before the 1992 FDA ban, implants were typically made of a silicone shell filled with silicone gel, with saline-filled implants being less popular. Currently, it is not known how many women have silicone vs. saline implants, but women with both types of implants are included in the NCI study.

3. What are the principal findings of the study?

  • The authors found no association between breast implants and the risk of subsequent breast cancer.
  • There was no association of breast cancer risk with years of follow-up.
  • Breast cancer risk was not associated with any particular type of implant.
  • Breast tumors tended to be detected at a somewhat later stage among breast implant patients than among the control group, but the difference was not statistically significant and could be due to chance.
  • There was no significant difference in breast cancer mortality between the implant and comparison patients.

4. Who are the participants in the study?

The participants include 13,500 women who had implant surgery for cosmetic reasons in both breasts before 1989. For comparison, about 4,000 women similar in age who had some other type of plastic surgery, such as removal of fat from the stomach or wrinkles from the face or neck, were identified. All participants were from 18 plastic surgery practices in six geographic areas (Atlanta, Ga.; Birmingham, Ala.; Charlotte, N.C.; Miami and Orlando, Fla.; and Washington, D.C.). The practices were chosen because the plastic surgeons had performed large numbers of cosmetic breast implant surgeries prior to 1989 and were willing to give the investigators access to their records.

5. What is the design of the study?

The medical records from the plastic surgery practices were reviewed to identify patients who were eligible for the study. For eligible patients, trained medical records abstractors collected information about the surgical procedures, the type of implant, anycomplications, and factors which might affect health status, such as weight or medical history.

Patients were then traced through a variety of sources. Living subjects were asked to complete a mailed questionnaire to collect information about their health status, including whether they had subsequent plastic surgery as well as lifestyle factors that could affect their health (menstrual, pregnancy, and breast-feeding history, weight, hormone use, cigarette smoking, alcohol consumption, and medical history). Extensive data on the potential short-term (rupture) and longer-term complications (cancer, connective tissue diseases, symptoms of connective tissue disease) were also obtained through the questionnaire.

No clinical examinations were done on the living patients for this study. Attempts were made to verify patient reports of cancer and connective tissue diseases by retrieving medical records from physicians who had diagnosed or treated these diseases. Death certificates were collected for the patients who had died to verify the causes of death.

About 80 percent of the original 13,500 implant patients and 4,000 controls were successfully traced. About 70 percent of those traced as alive completed the questionnaires. These percentages are similar to other comparably designed epidemiologic studies.

6. How do the characteristics of women with breast implants compare to women in the general population?

Previous studies have shown that breast implant patients are different from the general population in a number of ways. Some studies have reported that implant patients tend to have different reproductive and medical histories and different lifestyle characteristics.

7. How do the characteristics of the women in this study compare to other plastic surgery patients?

The authors of the current study published a paper in the March 2000 issue of Plastic and Reconstructive Surgery characterizing a subset of the participants. Data collected from 7,447 breast implant patients and 2,203 patients with other types of plastic surgery showed that implant patients were significantly more likely than other plastic surgery patients to be white, to have less education, to have early ages at first birth, to be thin, and to be screened frequently for breast disease. However, there were no differences between the two groups with respect to family income, number of pregnancies, alcohol consumption, cigarette smoking, histories of previous gynecologic operations, or operations for benign breast disease. Therefore, the authors believe that other plastic surgery patients may be a more appropriate comparison group than women in the general population for studies of the health effects of breast implants.

8. What is unique about this study?

This is one of the longest and largest studies to date on the health effects of breast implants. Most previous investigations have looked at the effects of implants over a shorter time period, typically less than 10 years. Besides the short follow-up periods, previous studies have been too small to evaluate rare diseases.

In addition, previous reports have not included information about types of devices implanted or risk factors affecting health, such as medical history, screening practices, and lifestyle behaviors (see question 5). All of these factors are included in the current NCI study.

Another unique feature of this study is that the investigators compared the breast cancer risks of the implant patients to both the general population and other plastic surgery patients. Previous studies have generally used only the general population for a comparison group, except for a recent Swedish study that compared women with implants to those with breast reduction procedures.

This information is produced and provided by the National Cancer Institute (NCI). References are available at their website at The information in this topic may have changed since it was written. For the most current information, contact the National Cancer Institute via or call 1-800-4-CANCER.

The contents of this health site are for informational purposes only. Always seek the advice of your physician or other qualified healthcare provider regarding any questions you may have about a medical condition.

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