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Epidemiology of Silicone-Gel Breast Implants

Brown, S. Lori

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Silicone breast implants may be classified as silicone-gel breast implants and inflatable saline breast implants. Silicone-gel breast implants were commercially available in the early 1960s, and saline breast implants became available in the 1970s. Multilumen implants combine a silicone-gel core with an outer saline lumen and are classified as silicone-gel implants because they contain silicone gel. Regardless of implant filling, the outer envelope is made of a silicone elastomer shell. The popularity of silicone breast implants has been unsurpassed in plastic surgery, and has been reported to be a mainstay of many plastic surgery practices. This presentation is principally about silicone-gel breast implants, but I will make reference to saline implants on occasion.

Regulatory History of Breast Implants

The Food and Drug Administration (FDA) did not have the authority to regulate medical devices, such as breast implants, until 1976 with the passage of the Medical Device Amendments. 1–3 In 1978, the General and Plastic Surgery Devices Panel (referred to as the Panel) recommended to the FDA that breast implants be classified as Class II medical devices, meaning that they had been established as safe and effective but required special measures to control their risks (special measures might include performance standards, postmarket surveillance studies, and user education). The FDA did not agree with this classification and classified breast implants as Class III devices, making the submission of premarket approval a requirement for implant manufacturers. Manufacturers submitted data in 1991 but after reviewing the data, the Panel voted that manufacturers had not provided adequate scientific data to support the safety and effectiveness of silicone-gel breast implants. The Panel recommended allowing silicone-gel breast implants to remain on the market while manufacturers collected the data for a complete submission for their product. However, in 1992, the Panel modified its recommendation on silicone-gel breast implants on the basis of continuing concerns over the lack of information on local complications with silicone-gel breast implants and the emerging concern that these implants might be associated with connective tissue disease (autoimmune disease). The Panel recommended that the availability of silicone-gel breast implants be restricted to women requiring them for reconstruction after cancer or other medical purposes while manufacturers collected data to support their safety and effectiveness. Manufacturers of inflatable saline breast implants were notified in January of 1993 that the agency would be requiring proof of the safety and effectiveness of their product. While the companies conducted the required studies, saline breast implants remained on the market. In May 2000, the FDA granted approval of two companies’ saline breast implant premarket applications.

Autoimmune disease was never the sole concern of the FDA (Table 1). In several reports published at the time that silicone-gel breast implant use was restricted, the FDA explicitly stated that there were concerns with local complications such as breast implant rupture, capsular contracture (a fibrous scar capsule forms around the implanted prostheses and may contract causing pain and breast deformity), infection, chronic pain, interference with mammography, and other local complications. 4,5

Table 1
Table 1:
Local and Systemic Complications Attributed to Breast Implants

In 1992–1993, the FDA received a flood of 50,185 adverse event reports on silicone-gel breast implants from implant manufacturers and others. 6 Of the 94,120 adverse event reports on silicone-gel breast implants sent to the FDA between 1984 and 1995, 26.5% reported implant rupture and an additional 10.4% reported capsular contracture. Many other reports described capsular contracture but these had been coded as “reactions” so were not included in the tabulation of capsular contracture. Although the FDA had received thousands of reports on adverse events, there were still no reliable estimates of incidence or prevalence of local complications in women with breast implants. In 1992, there were not even population-based appraisals of the prevalence of breast implants in women in the United States.

Prevalence of Breast Implants in the United States

Several reports have estimated the prevalence of breast implants in the United States. A study by Bright et al (1993) 7 utilized National Health Interview Survey data from the National Center for Health Statistics and estimated that 304,000 (95% confidence interval = 239,000–369,000) adult women had breast implants by 1988. However, this questionnaire survey likely underestimated the prevalence of implants because the wording of the question implied that only implants used for medical purposes should be reported. Marketing estimates have suggested that only 20% of implants have been used for reconstruction or other medical purposes and that 80% were for cosmetic augmentation. Furthermore, because the questionnaire respondent could be any household resident over the age of 18, it is likely that some respondents were not aware of breast implants that other family members had. Bright has updated her estimate, on the basis of marketing data, to 1.2 million women by 1991. 8 A recent study by an implant manufacturer estimated that by 1989 there were 815,700 women with breast implants (95% CI = 715,757–924,729). 9 This study was based on responses by 28,264 households to 40,000 mailed surveys. A third recent study estimated that 894,206 U.S. women (95% CI = 437,602–2,035,783) had cosmetic breast implants between 1963 and 1988 based on computer simulation of data from a New York state historical cohort. 10 None of these studies distinguishes between silicone-gel and saline implants.

Systemic Illness: Autoimmune Disease and Cancer in Women with Implants

By 1992, there were numerous case series in the literature describing women with breast implants and autoimmune disease. 11 These case series described scleroderma, systemic sclerosis, morphea, rheumatoid arthritis, mixed connective tissue disease, systemic lupus erythematosus (SLE), polymyositis, and fibromyalgia in women with breast implants or silicone injections, but there were no studies that compared the occurrence of these diseases in women with exposure to silicone to unexposed women. This lack of epidemiologic studies made evaluation of claims that implants were causing connective tissue disease impossible to assess. In 1994, a study based on a retrospective medical record review of 749 women with breast implants and 1,498 women without implants indicated that there was not a difference in the occurrence of connective tissue disease overall in women with implants. 12 However, as the authors of this study stated themselves, the small study size “had limited power to detect an increased risk of rare connective-tissue disease such as systemic sclerosis” and that they had calculated that “it would require a sample of 62,000 women with implants and 124,000 women without implants, followed for an average of 10 years each, for a doubling of the relative risk of this condition [systemic sclerosis] to be detected...”12 Another retrospective cohort study with a much larger sample size (395,543 women) depended on self-report of connective tissue disease by women. In this study, the relative risk of connective tissue disease in the 10,830 women with breast implants was significantly increased to 1.24 (95% CI = 1.08–1.41). 13 Relative risks of individual connective tissue diseases [scleroderma 1.84 (95% CI = 0.98–3.46), dermatomyositis or polymyositis 1.52 (95% CI = 0.97–2.37), Sjögren’s syndrome 1.49 (95% CI = 0.97–2.28), and rheumatoid arthritis 1.18 (95% CI = 0.97–1.43)] were also increased in women with implants, albeit these were not statistically significant. A retrospective cohort study of women in the Swedish national inpatient registry implanted between 1964 and 1993 included 7,442 women with breast implants either for cosmetic or reconstructive purposes. 14 In this study, 3,353 women undergoing breast reduction surgery were the comparison group. The outcome examined was hospitalization for definite connective tissue disease including rheumatoid arthritis, SLE, systemic sclerosis, dermatomyositis, and Sjögren’s syndrome. The study concluded that there was no excess in connective tissue disease-related hospitalizations of women with breast implants as compared with women who underwent breast reduction surgery. This study addressed the issue of severe connective tissue disease that resulted in hospitalization, but it did not address the issue of increased connective tissue disease overall. A similar study performed in Denmark examined hospital discharge rates of women with implants for cosmetic or reconstructive purposes 15 and reported that women with breast implants were no more likely to be hospitalized for these diseases than were the comparison groups. Another study included a blinded clinical assessment of a historical cosmetic breast augmentation cohort and a comparison cohort of women undergoing other cosmetic surgery not involving silicone identified from a provincial registry in Alberta, Canada. 16 In this study, women self-reporting connective tissue disease or symptoms, past visits to rheumatologist or other relevant specialists, or the use of drugs typically prescribed for connective tissue disease were invited to undergo a clinical assessment. Prevalence rates for rheumatoid arthritis, SLE, scleroderma, and Sjögren’s syndrome were no higher in women with breast implants than in the comparison group. However, women with breast implants were more likely to report symptoms such as muscle pain, hand pain, and numbness in the extremities than were women in the comparison group. Others have also reported that women with breast implants were more likely to report symptoms such as painful joints for at least 3 months than were age-matched cosmetic surgery controls. 17

Several case-control studies have explored the association between breast implants and scleroderma. 18–20 Adjusted odds ratios from these studies put the risk of developing scleroderma for women with breast implants at 1.00 (95% CI = 0.16–6.16), 18 1.07 (95% CI = 0.55–2.24), 19 and 1.30 (95% CI = 0.27–6.23). 20 Each of these studies has concluded that breast implants are not associated with scleroderma. A case-control study of SLE included ascertainment for breast implants or “injections” to increase breast size, making interpretation of this study difficult. 21 Because none of the controls had breast implants, it was not possible to calculate an odds ratio from this study. However, compared with the controls from a cancer case-control study, the calculated odds ratio was 4.5 (90% CI = 0.2 - 27.3). A case-control study based on Medicare claims data examined the relationship of silicone implants (not breast implants) to connective tissue disorder and reported significant associations between silicone implants and SLE with an odds ratio of 1.68 (95% CI = 1.16 - 2.43), rheumatoid arthritis 8.96 (95% CI = 7.64–10.50), polyarthritis 4.47 (95% CI = 3.30–6.06), Sicca syndrome 2.26 (95% CI = 1.39–3.69), and ankylosing spondylitis 3.43 (95% CI = 1.96–5.98). 22

After reviewing these and numerous other studies 11,23 we concluded that these studies, taken together, indicate that there is not a large increase in connective tissue disease in women with breast implants; however, these studies do not rule out a small but significant increase in connective tissue disease overall, nor can they rule out an increased relative risk of specific rare connective tissue disease in women with breast implants. As described previously, these studies do not address the issue of an atypical syndrome in women with breast implants. 11,23 Like the FDA, several commissioned panels have reviewed currently available publications on connective tissue disease and breast implants and drawn similar conclusions, albeit the Institute of Medicine concluded emphatically that epidemiologic evidence suggested that there was no atypical syndrome in women with implants (Institute of Medicine, National Science Panel, and Independent Review Group). 24–27

Implantation of silicone had been of concern because of the observation that implanted materials could be involved in a phenomenon described as solid-state tumor formation in rodents. Breast cancer was of concern because of implant location, but numerous studies have failed to find an increased risk for breast cancer in women with breast implants. 28–31 However, we have concluded that carcinogenic effects of breast implants on other sites has not been precluded. 32 For instance, an increase in both vulvar and lung cancer were observed in women with breast implants, 15 but because this study was a linkage study, it was not possible to adjust for potential confounders. We have reviewed these and other studies on cancer risk in women with breast implants 32 and concluded that, based on currently available studies, there is not evidence that implants either increase or decrease the risk of breast cancer and that, although currently published studies have not shown that there is an increased risk for other types of cancers in association with breast implants, more study is needed to address this issue adequately. Likewise, The International Agency for Research on Cancer has recently concluded, “There is evidence suggesting lack of carcinogenicity in humans of breast implants, made of silicone, for female breast carcinoma,” and “There is inadequate evidence in humans for the carcinogenicity of implanted prostheses made of silicone for neoplasms other than female breast carcinoma.”33 The Institute of Medicine concluded that “... the available evidence does not support an association of silicone or silicone breast implants with experimental carcinogenesis (other than rodent solid-state carcinogenesis), primary or recurrent breast cancer, breast sarcoma or other solid tumors, lymphoma, or myeloma.”24

Breast Implants and Local Complications

In contrast to systemic disease in which causal associations are largely determined by statistics, local complications associated with breast implants are related to the breast implant or implant surgery; they do not occur in women without implants (Table 1). The Institute of Medicine concluded that “ ... local and perioperative complications are frequent enough to be a cause of concern and to justify the conclusion that they are the primary safety issue with silicone breast implants. Complications may have risks themselves, such as pain, disfigurement and serious infection and they may lead to medical and surgical interventions, such as reoperations, that have risks.”24

The plastic surgery literature describes the complications associated with breast implants, but information on the rates or typical severity of most of these complications is not available. Obviously, decisions to have breast implant surgery cannot be informed decisions if neither physicians nor patients are able to assess the likely occurrence of complications nor their typical severity. How often does capsular contracture occur, and how often does the patient have implants explanted (additional surgery) because of the capsular contracture? How likely are women to have breast or chest pain, and how often do women have implants removed because of pain? How often are breast implants extruded (through the skin), and what are the risk factors for extrusion? Are surgical infections more common in mammaplasty than in other breast surgeries? Are infections more common with breast implants than with other implants? How often do late infections occur, and what is the source of the infection? How often do implants rupture, and are women at increased risk for other complications (local or systemic) when implants rupture? When silicone-gel breast implants rupture, how likely is it that the gel will migrate? These and many other questions about local complications and their impact remain unanswered.

One population-based study described local complications that resulted in additional surgeries. 34 In this study, during a short follow-up period with a mean of 7.8 years, 27.8% of women underwent at least one additional surgery. The most frequent reason for surgery in women was capsular contracture (17.5%), and women with mastectomies were more likely to have complications leading to resurgeries than women having implants for purposes of cosmetic augmentation. Capsular contracture, the painful hardening of the fibrous scar that forms around breast implants, has been a frequent local complication for women with breast implants. 6,35

An issue of particular concern to the FDA has been breast implant rupture. 36 Silicone-gel breast implant rupture may not always be clinically apparent, as indicated in a study in which retrospective review of mammograms revealed that 5% of implants had ruptured without being apparent to women. 37 Because mammography is the least sensitive method for detection of implant rupture, 38 it is likely that the prevalence of silent rupture is higher than this. Other studies have relied on observing the prevalence of disruption (ruptured or leaking) for explanted implants and have reported implant disruption rates ranging from 23% to 67%. 39–45 However, some have argued that because these studies feature a population of women who are having implants explanted because they are having problems with their implants, the high rates from these studies are not representative of women with implants in general.

To address some of these issues and to provide physicians and women with information on the prevalence of rupture in an unselected population, the FDA initiated a study of silicone-gel breast implant rupture. This study will include 1,247 women with breast implants identified as part of a National Cancer Institute cohort. 46 Women were called and asked to recall surgeries involving removal and replacement of their implants. Women who reported implant removal were asked to recall whether they were told if their implant(s) were ruptured or intact when removed. We also sought permission from women to examine the surgical record from reported surgeries for notes indicating the status of the implants when they were removed. A sample of women with silicone-gel breast implants were invited to have a magnetic resonance imaging examination of their breasts to determine whether their current implants are intact or ruptured. Information from these multiple sources has given us a more complete picture of the prevalence of implant rupture in an unreferred population. One-third of the women in the FDA study reported that they underwent at least one additional surgery after their first surgery to place breast implants and a majority (77%) of the 344 women in the FDA study who underwent a magnetic resonance imaging examination were found to have an implant that was either ruptured or suspicious for rupture. 47


Silicone breast implants have been available in the United States for more than 30 years, but there are still many questions about their safety and effectiveness. The FDA has fewer concerns about an association between breast implants and connective tissue disease or breast cancer than in 1992 because of epidemiologic studies that have addressed these issues. Information on rates or prevalence of local complications is limited but is important for physicians and women to make informed decisions about implants. The FDA has conducted a study to assess breast implant rupture prevalence in an unselected population of women with implants.


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breast prostheses; silicone; implants

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