Silicone Breast Implants Not Linked to Most Cancers

National Cancer Institute
Tuesday, 24 April 2001

Reporting in the April issue of the Annals of Epidemiology*, researchers from the National Cancer Institute (NCI) in Bethesda, Md., found that women with silicone breast implants were not at increased risk for most cancers. Although they did find small increases in the risks for respiratory (cancers of the lung and larynx) and brain cancers, the significance of these findings is not clear.

The participants were from 18 plastic surgery practices and included 13,500 women who had implant surgery for cosmetic reasons and, for comparison, 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. The average length of follow-up was 13 years.

Besides the large number of participants and extended follow-up, another strength of this study is that unlike previous reports, it included information about lifestyle factors that could influence a woman's risk of subsequent disease. In addition, the cancer risks of the implant patients were compared to two separate control groups: the 4,000 plastic surgery patients and the the general population.

The researchers previously showed that other plastic surgery patients are a more appropriate comparison group than the general population because of certain similarities between the two groups. These include the number of pregnancies, previous gynecologic operations, and operations for benign breast disease, as well as the levels of alcohol consumption and rates of cigarette smoking.**

When the cancer rates among the implant patients were compared to the 4,000 other plastic surgery patients, the rates for nearly every cancer, including mouth, stomach, large intestine, breast, cervix, uterus, ovary, bladder, thyroid, connective tissue, and immune system were not increased among implant patients.

Prior anecdotal reports suggested that implant patients may have increased risks for tumors that develop from connective tissue, such as soft tissue sarcomas, or for cancers of the immune system, such as lymphomas and leukemia. However, the NCI researchers did not find an increased risk of sarcomas among implant patients, nor did Hodgkin's or non-Hodgkin's lymphoma develop at higher rates. Further, no increased risks were seen for multiple myeloma. This disease was a concern because an earlier laboratory study reported that mice injected with silicone gel developed tumors derived from the same kind of cell as multiple myeloma (plasma cells or B-cells -- cells of the immune system that make antibodies).

Although the incidence of leukemia was nearly twice as great among implant patients, this appears likely to be a chance finding because the wide variety of leukemia types in the eight observed cases (vs. two in the plastic surgery controls) tends to rule out a single cause such as exposure to silicone. A smaller 1998 Swedish study reported a small increased risk of leukemia, but it was based on only three cases, so this may have been a chance finding.

The only cancers that were greater in the implant group compared to the plastic surgery control group were respiratory and brain cancers. The rates were between two to three times greater, and only the rates of respiratory cancers reached statistical significance. However, it ispossible that the higher risks observed for respiratory and brain cancers are not related to exposure to silicone, but are due to either chance findings or to factors common to women who choose to have implants.

The increased risk of respiratory cancers was mainly due to the large number of lung cancers cases (33 in the implant patients vs. 13 in the other plastic surgery patients), and is difficult to interpret. Because most of the respiratory cancers were found through death certificates, the role that smoking played in development of the cancers is not clear, since information about lifestyle factors was obtained through a questionnaire administered to living participants. However, among the living participants, there was no significant difference between the smoking rates of implant patients and plastic surgery controls. Two previous reports with cosmetic implant patients found smaller increased risks of respiratory cancers compared to the general population, although these studies had small numbers of participants, limited follow-up, and little data on smoking habits.

There is no obvious explanation for the increased risk of brain cancers. Eleven cases of brain tumors among the implant patients were identified on death certificates as the cause of death compared to one case in the plastic surgery control group. Most of the tumors were classified as glioblastoma multiforme. The researchers could find no distinctive cellular characteristics in the tumors to suggest they were related to exposure to silicone. Brain cancer has not been previously linked to breast implants, and the reason for the increased risk in this study remains unclear.

When the NCI researchers compared the risks for the implant patients with the general population, they found that the implant patients were two to three times more likely to develop stomach cancer, leukemia, and cancers of the cervix, vulva and brain.

Previous breast implant studies also reported an increased risk of cancers of the cervix and vulva compared to the general population. However, unlike the current one, these studies were small (less than 1,000 patients), and included less than 10 years of follow-up, without information on lifestyle factors that may contribute to these tumors, such as socioeconomic status, sexual and reproductive behavior, and cigarette smoking. Therefore, it is possible that the increased risk of these cancers was related to factors common to women undergoing plastic surgery rather than to the effects of silicone exposure.

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. About 80 percent are for cosmetic reasons and 20 percent for breast reconstruction after breast cancer surgery. The current study does not include patients who received implants after a diagnosis of breast cancer.

The NCI scientists reported last year that the implant patients had no change in their risk of breast cancer compared to both control groups.*** Further analyses of the data will evaluate the risks associated with various causes of mortality and the risk of developing connective tissue disorders.

*The study is titled "Cancer Risk at Sites Other than Breast Following Augmentation Mammoplasty." The authors are Louise A. Brinton, Jay H. Lubin, Mary Cay Burich, Theodore Colton, S. Lori Brown, and Robert N. Hoover. Annals of Epidemiology, April 2001;11(4):248-256.

**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, and Jay H. Lubin. Plastic and Reconstructive Surgery 2000;105(3):919-27.

***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.

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