In one of the largest studies on the long-term health effects of silicone breast implants, researchers from the National Cancer Institute (NCI) in Bethesda, Md., found no association between breast implants and the subsequent risk of breast cancer. The study is published in the November issue of Cancer Causes and Control.*
Breast implants first appeared on the market in 1962. Manufacturers initially assumed that the implants were biologically inactive and, therefore, would have no harmful effects. However, over the past two decades there have been a number of reports of connective tissue disorders and cancers among implant patients.
In 1992, because of the lack of sufficient evidence on the long-term safety of implants, the Food and Drug Administration (FDA) restricted the use of silicone breast implants to women seeking breast reconstruction in controlled clinical trials, and Congress directed the National Institutes of Health to undertake a large follow-up study to evaluate the long-term health effects of the implants.
"This is the first part of our analysis of the health risks from the study," said
Louise A. Brinton, Ph.D., principal investigator from NCI's Division of Cancer Epidemiology and Genetics (DCEG) in Bethesda, Md. "For women followed for more than 10 years, there was no change in breast cancer risk. Our results do not confirm the findings from several other studies that exposure to implants reduces a woman's risk for breast cancer. This may relate to the longer follow-up in this study as compared with most others."
The average length of follow-up was 12.9 years among the implant patients and
11.6 years among the comparison patients. In previous studies, women with implants were generally followed for less than 10 years.
The participants included 13,500 women who had implant surgery for cosmetic reasons in both breasts sometime between 1962 and 1989 and, 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 and neck. Both groups of women were selected from 18 plastic surgery practices in which the surgeons had performed large numbers of cosmetic breast implant surgeries prior to 1989 and were willing to give the investigators access to their records. The practices were located in six geographic areas: Atlanta, Ga.; Birmingham, Ala.; Charlotte, N.C.; Miami and Orlando, Fla.; and Washington, D.C.
In order to carry out the study, researchers reviewed the medical records from the plastic surgery practices and collected data about the surgical procedures, types of implants, and complications, if any, as well as factors affecting health status, such as weight and medical history. Patients who were located were asked to complete a mailed questionnaire in order to collect information about their health status, factors that might affect their health, and short- and long-term complications that might be associated with the implants. No clinical exams were done on the patients, but attempts were made to verify patient reports of cancer and connective tissue disease from the medical records of the physicians who diagnosed or treated the diseases. For patients who had died, death certificates were collected to verify the causes of death.
Besides the size of the study and the length of follow-up, another unique feature of the NCI study is that the researchers compared the breast implant patients to both the general population and to women who had received other types of plastic surgery. In previous reports, the general population was used as the control group. However, NCI investigators found in an earlier study** that women with 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 histories of previous gynecologic operations and operations for benign breast disease. Therefore, they believe that women who received other types of plastic surgery may be a more appropriate comparison group than the general population. However, when compared to either the general population or women with other types of plastic surgery, there was no evidence of a change in breast cancer risk in the implant group.
Typically, implants are soft silicone sacs, inflated with either saline solution (salt water) or a synthetic silicone gel. Both have been marketed since 1962. Before the 1992 FDA ban,
90 percent to 95 percent of the implants contained silicone gel because they had a more pleasing look and feel than the saline-filled implants. Since 1992, 90 percent to 95 percent of the implants have been saline-filled. It is not known how many women currently have silicone vs. saline implants.
Of the implant patients in the study, 49.7 percent received silicone gel implants,
34.1 percent double lumen implants, 12.2 percent saline-filled implants, 0.1 percent other types of implants, and 3.8 percent unspecified types of implants. (Double lumen implants have two shells; the inner sac is filled with silicone gel and the outer with saline.) The participants had cosmetic surgery during a time (between 1962 and 1988) when a great number of changes were taking place in the manufacturing of breast implants such as the shell thickness, the type of shell coating, and the gel composition. However, the researchers found there was no altered breast cancer risk associated with any of the types of implants.
One of the controversial issues is whether women with breast implants have more advanced breast cancer at diagnosis than women without implants. In the current study, NCI researchers found a somewhat later stage at detection of breast cancer among the implant patients compared to the controls and a smaller percentage of in situ (early-stage) cancers among the implant patients. However, the differences were not statistically significant and there was no significant difference in breast cancer mortality between the implant and comparison group.
"This is an issue that needs further study," said Brinton. "This would include continuing to follow participants in this study to see if their breast cancer death rate changes with time."
About 80 percent of breast implants in the United States are for cosmetic reasons and
20 percent for breast reconstruction. This study does not include women undergoing breast reconstruction after breast cancer surgery, so it is not possible to predict whether similar results would be found for this population. The majority of the previous studies have also focused on women who received implants for cosmetic reasons.
It is estimated that between 1.5 million and 2 million U.S. women have had breast implants since they first appeared on the market in 1962.
Future analyses of the data will evaluate the risk of other cancers, connective tissue disorders, and causes of death.
*The study is titled, "Breast Cancer Following Augmentation Mammoplasty (United States)." The authors are Louise A. Brinton, Jay H. Lubin, Mary Cay Burich, Theodore Colton,
S. Lori Brown, and Robert N. Hoover. Cancer Causes and Control 2000; Vol.11(9):819-827.
**The study is titled: "Characteristics of a Population of Women with Breast Implants Compared with Women Seeking Other Types of Plastic Surgery." The authors are
Louise A. Brinton, S. Lori Brown, Theodore Colton, Mary Cay Burich, Jay H. Lubin.
Plastic and Reconstructive Surgery 2000;105(3):919-27.