© The Author 2006. Published by Oxford University Press.
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Long-Term Cancer Risk Among Swedish Women With Cosmetic Breast Implants: An Update of a Nationwide Study
Affiliations of authors: International Epidemiology Institute, Rockville, MD (JKM, LL, JPF, RET, ON); Department of Medicine (JKM, JPF, RET, ON), Department of Preventive Medicine (LL), Vanderbilt University Medical Center, Vanderbilt-Ingram Cancer Center, Department of Medical Epidemiology and Biostatistics, Nashville, TN; Karolinska Institutet, Stockholm, Sweden (WY, ON)
Correspondence to: Joseph K. McLaughlin, PhD, International Epidemiology Institute, 1455 Research Blvd., Suite 550, Rockville, MD 20850 (e-mail: jkm{at}iei.ws).
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ABSTRACT |
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Epidemiologic evidence does not support a consistently increased cancer risk among women with cosmetic breast implants, but few studies have assessed risk beyond 15 years. Swedish women who underwent cosmetic breast implantation for the first time between January 1, 1965, and December 31, 1993 (N = 3486), were followed through December 31, 2002. Cancer incidence was ascertained through the nationwide Swedish Cancer Registry. Standardized incidence ratios (SIRs) and 95% confidence intervals (CIs) were calculated to compare cancer incidence of women with implants with women in the general population. Mean follow-up among women with breast implants was 18.4 years (range = 0.1–37.8 years). The incidence of breast cancer was below expectation (SIR = 0.7, 95% CI = 0.6 to 1.0), whereas lung cancer was above expectation (SIR = 2.2, 95% CI = 1.3 to 3.4). With respect to cancer overall and all other specific cancer sites, including brain cancer and sarcoma, non-Hodgkin lymphoma, and multiple myeloma, no statistically significantly increased or decreased SIRs were observed. Stratification by duration of follow-up revealed no statistically significantly increased or decreased SIR, with the exception of a two- to threefold excess of lung cancer among women followed for more than 15 years, which would be expected due to the high prevalence of smoking among the Swedish women with implants in our study.
Numerous epidemiologic studies have examined the association between cosmetic breast implants and the incidence of cancer (1–13). The primary concern, which has arisen from anecdotal reports, has been increased breast cancer risk, but some early studies also raised concern that women with breast implants may be at risk of developing other cancers, including lung cancer, cancers of the cervix and vulva, lymphoma, and multiple myeloma. However, the International Agency for Research on Cancer concluded that silicone implants are not carcinogenic in breast tissue (14), and several other independent scientific review bodies have unanimously concluded that there is no demonstrated excess of cancer of any type among women with cosmetic breast implants (15–17).
Despite the general consistency of the epidemiologic evidence, a single study has reported an increased risk of death from brain cancer among women with breast implants compared with women in the general population (18). However, the findings are hampered by methodologic shortcomings (19). No other epidemiologic study of women with breast implants has confirmed this excess of brain cancer (6,11–13,19).
We have extended our earlier nationwide cohort study of Swedish women with cosmetic breast implants (11) to provide an additional 9 years of follow-up. Thus, our investigation provides data on the longest large-scale follow-up of women with cosmetic breast implants to date.
This study was conducted in Sweden using essentially complete nationwide population and health care registers, including the Swedish Inpatient Register (IPR), Cancer Register, Death Register, Migration Register, and Register of the Total Population. Unique personal identifiers (national registration numbers) assigned to each Swedish resident allowed record linkage between these registers with few losses to follow up. The study was approved by The Regional Ethics Committee of Sweden. Additional details about study methods have been presented elsewhere (11,20).
The Swedish IPR, which was established in 1964 and became nationwide in 1987, records information on all hospital admissions (21). Each IPR record contains (a) the patient's national registration number, (b) the date of hospital admission and discharge, (c) one primary discharge diagnosis and up to seven additional diagnoses coded according to the 7th Revision of the International Classification of Diseases (ICD-7) until 1968, ICD-8 from 1968 through 1986, ICD-9 from 1987 to 1996, and ICD-10 thereafter, and (d) up to 12 surgical codes classified according to the Swedish Classification of Operations until 1996 and the Nordic Medico-Statistical Committee's Classification of Surgical Procedures thereafter. This study was based on 3486 women who were identified through the IPR and who underwent cosmetic breast implantation for the first time between January 1, 1965, and December 31, 1993.
Through linkage to the Cancer, Death, and Migration Registers, women in the breast implant cohort were followed for the occurrence of cancer from 30 days after the date of first cosmetic breast implantation until date of emigration, date of death, or 31 December 2002, whichever occurred first. Information on cancer diagnoses (ICD-7) was obtained from the Swedish Cancer Register, which has recorded the incidence of cancer on a nationwide basis since 1958 and has been shown to have an accurate and virtually complete ascertainment of cancer patients (22). The current report is based on 28 627 additional person-years of follow-up and 106 additional cancers compared with the previous report from this cohort (11).
The number of cancer patients observed among women in the breast implant cohort was compared with that expected in the general female population of Sweden. Age-, sex-, and calendar year-specific person-years were multiplied by the corresponding cancer incidence rates for Sweden to determine expected numbers. Standardized incidence ratios (SIRs) and exact 95% confidence intervals (CIs) were calculated for all cancers combined and for specific sites assuming a Poisson distribution for observed cancers (23).
Characteristics of the cohort of 3486 women with breast implants are presented in Table 1. The average age at breast implant surgery was 32 years. Women with breast implants were followed for more than 64 000 person-years, with a mean follow-up of 18.4 years (range = 0.1–37.8 years). Approximately 65% (n = 2255) of women in the cohort were followed for 15 years or more after breast implantation, and 21% (n = 741) were followed for at least 25 years.
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Overall, we observed 180 cancers among women with breast implants compared with 193.1 expected based on general population rates (SIR = 0.9, 95% CI = 0.8 to 1.1) (Table 2). The incidence of breast cancer was below expectation (SIR = 0.7, 95% CI = 0.6 to 1.0) based on 53 observed case patients. There was an excess of lung cancer among women with implants, with 20 case patients observed compared with 9.1 expected (SIR = 2.2; 95% CI = 1.3 to 3.4).
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No statistically significantly increased or decreased SIRs were observed for any other site-specific cancers. In particular, the SIR for brain cancer was 1.3 (95% CI = 0.6 to 2.3) based on 11 observed case patients. Among the 1355 women (38.9% of the cohort) with 20 or more years of follow-up since implant surgery, there was one brain cancer observed compared with 0.87 expected. The incidences of both non-Hodgkin lymphoma (n = 3; SIR = 0.7; 95% CI = 0.1 to 1.9) and multiple myeloma (n = 1; SIR = 0.7; 95% CI = 0.0 to 4.1) were both within expectation. None of the observed patients with non-Hodgkin lymphoma had primary origin in the breast. Two patients with sarcoma were observed among women with implants, and neither cancer was located in the breast; one was a lower limb liposarcoma, and the other was in the connective tissue of the thorax, abdomen, or pelvis.
SIRs for cancer overall and for breast and lung cancer were stratified by time since breast implantation (Table 3). Almost 50% of the observed cancers occurred among cohort members who were followed for at least 15 years after breast implantation. For cancer overall and for the two specific sites examined, none of the SIRs was statistically significantly increased or decreased during any of the follow-up periods, with the exception of a two- to threefold excess of lung cancer among women followed for more than 15 years after implantation.
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This nationwide population-based cohort study of Swedish women with cosmetic breast implants extends the follow-up of our earlier study by almost 10 years and more than doubles the number of cancers observed. This is the longest follow-up study of women with breast implants published to date, and it includes more than 2200 women (65% of the cohort) who were followed for 15 years or more after breast implantation and over 700 women (21% of the cohort) who were followed for at least 25 years. Our results reflect those of numerous other epidemiologic studies and are generally consistent with independent review panels in finding no increased risk for breast or other cancers among women with cosmetic breast implants. The only exception was our finding of an increased risk for lung cancer among women with implants, but this excess reflects the higher prevalence of smoking among Swedish women with implants compared with the general population.
Although biologic mechanisms by which implants might reduce breast cancer risk have been hypothesized (3,6,24), there are several more likely explanations for the consistently reduced incidence of breast cancer among women with breast implants found in this and most other studies. It has been demonstrated that women who undergo breast implantation have certain underlying characteristics that may put them at a lower risk for breast cancer, including younger age at first birth, higher parity, and lower body mass index (25–28). We did not have information on reproductive characteristics of women in our cohort, but a recent cohort study of Danish women with breast implants found that the reduction in breast cancer risk persisted after adjustment for age at first birth and number of children (12). It is also plausible that women who are diagnosed with breast cancer during preoperative screening before breast implantation, as well as women with a family history of breast cancer, are underrepresented in cohorts of women with cosmetic breast implants, thereby decreasing the incidence of breast cancer in these cohorts compared with women in the general population. Finally, a potential alternative explanation could be underascertainment or delayed detection due to the implant itself, but numerous studies have shown that women with implants are not diagnosed with more advanced stages of breast cancer or experience shorter survival than women without implants (12,29–32).
Consistent with the results of virtually all other epidemiologic studies on this topic (19), we did not observe a statistically significant excess risk for brain cancer among women with implants. Hence, we found no support for the single study that has reported this association (4,18). Recently, an update of that cohort found that the risk for brain cancer was attenuated and no longer statistically significant (33).
As in the previous report from this study (11), we observed a statistically significant increase in lung cancer risk among women with breast implants, which is likely to be explained mostly by the higher prevalence of smoking among the cohort of women with implants compared with Swedish women in the general population. An earlier study (25), based on a subset of the present cohort, found that women with implants were 2.8 times more likely to be current smokers than the general Swedish female population. A greater than twofold higher prevalence of smoking has also been reported among Danish women with cosmetic breast implants compared with the general female Danish population (26).
Concerns about multiple myeloma, sarcoma, and lymphoma among women with breast implants have been raised as a result of animal studies and uncontrolled case series (34–37), but these hypotheses have not been supported by epidemiologic studies of women with breast implants. Only three women in our cohort developed non-Hodgkin lymphoma and one developed multiple myeloma, both below expected numbers based on cancer incidence rates in Sweden. Similarly, we observed only two sarcomas in more than 64 000 person-years of follow-up, and neither of the tumors was in the breast.
The study has potential limitations. Although the cohort is relatively large, the risk estimates for rare cancers of a priori interest, including sarcoma and multiple myeloma, suffer from low precision.
In addition to the long follow-up (up to 37 years), the strengths of our study include the cohort design, the nationwide population-based approach, and the computerized linkage of cohort members to the Swedish Cancer Registry, which virtually eliminates loss-to-follow-up and minimizes the possibility of information bias.
In conclusion, the results of our study are generally consistent with those of earlier epidemiologic studies and independent reviews in demonstrating no increased risk for breast or other cancers among women with cosmetic breast implants, with the exception of an observed excess of lung cancer, which would be expected due to the much higher prevalence of smoking among the Swedish women with implants. This is the longest follow-up study of women with breast implants to date. After an average follow-up of 18 years and a maximum follow-up of 37 years, we found that women who have undergone breast implantation have a reduced risk for breast cancer, most likely due to differences in lifestyle or reproductive characteristics. We also found no increased risk for brain cancer or for lymphoma, sarcoma, or multiple myeloma.
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NOTES |
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TopNotesAbstractReferences |
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Funded by the International Epidemiology Institute, which in turn received funds from the Dow Corning Corporation.
The Dow Corning Corporation was not involved in any aspect of the study design, data collection, data analysis, interpretation, or the writing of the manuscript.
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