Industry Associations:
Breast Silcone Implant
By Dr. Mark P. Kohout Published: 11/03/2010
Breast Silicone Implant
Introduction
The U.S. Food and Drug Administration (FDA)
published a Final Rule for silicone gel-filled breast
prostheses (April 10, 1991) and a Proposed Rule
for saline inflatable breast prostheses. In these
rules, the Agency listed a variety of risks that it
believed were potentially associated with the use
of these devices.
This document provides a critical review of
pertinent information concerning the safety of
silicone gel-filled and saline-filled mammary
prostheses, covering each of these identified risks,
as well as the recently publicized issue of potential
health effects in breastfed children.
Fibrous Capsular Contracture
Capsule formation is a normal wound healing
process that commonly occurs within the first
few months of surgery. The fibrous tissue capsule
isolates the implant from the surrounding tissue.
In some instances the capsule contracts around
the implant causing the breast to become firm,
and in severe cases, painful and distorted. The
subjectively defined Baker scale has been widely
used by the medical profession as a measure of
capsular contracture severity. When the Baker
scale is used to evaluate fibrous capsular contracture
(FCC), only Grade III and Grade IV contractures
are identified as “clinically significant”.
FCC can develop on one or both sides. To date,
no single factor has been demonstrated to be the
sole cause of contracture. The range of potential
causal factors includes non-specific and specific
foreign body reaction, periprosthetic infection,
haematoma, inadequate surgical dissection, and a
variety of others. It is likely that the development
of FCC is multifactorial.
Capsular contracture appears to be minimized by
textured surface prostheses.
For saline-filled mammary prostheses, the
estimated average incidence of Grades III and
IV contracture is approximately five percent. A
recent prospective study of saline-filled mammary
prostheses with a textured surface reported
a significantly lower incidence of clinically
significant FCC of approximately two percent.
An estimate of the average incidence of Grades Ill
and IV contracture for silicone gel-filled prostheses
with textured shells is approximately 1%-5%.
The incidence of all grades of contracture has
been steadily decreasing since silicone gel-filled
implants were first introduced.
Silicone gel leakage & migration
Leakage and migration of silicone gel from
silicone gel-filled mammary prostheses has been
shown to occur. Gel leakage can result from either
rupture of the envelope or passage of minute
amounts of gel through the silicone envelope (“gel
bleed”). Migration of the silicone gel involves the
movement of gel released from the breast implant
to distant locations in the body.
Rupture of silicone gel-filled mammary prostheses
is an infrequent event that in the majority of
cases has resulted from external capsulotomy.
Reported incidence rates for rupture range
from 0.5 to 6.6 percent. There is no conclusive
evidence to suggest that minute amounts of gel
bleed from silicone gel-filled prostheses represent
a risk. The incorporation of “low bleed” shells
containing a barrier membrane in breast implants
manufactured over the last ten years has still further
reduced the small amounts of gel that might
bleed from an implant. Further, although silicone
lymphadenopathy and silicone granulomas may
occur in cases of gel bleed or implant rupture,
in most cases gel bleed represents an incidental
finding of no clinical significance.
Rupture and deflation of saline
breast prostheses
Rupture and deflation of saline-filled mammary
prostheses have been reported to occur hours to
years after surgery. The release of the saline from
the ruptured device poses no known risks to the
patient; nevertheless, such rupture generally leads
to reoperation to remove or replace the prosthesis.
Several potential contributing factors for rupture
and deflation have been proposed, including
composition and structure of early devices, foldflaw
failure, closed capsulotomy, and surgical
factors. In the published literature, the reported
historical incidence of deflation of saline-filled
mammary prostheses is highly variable ranging
from 0 percent to 76 percent (average 5%) on
a per patient basis. As a result in improvements
in prosthesis design over the years, the incidence
rate for deflation has decreased. The approximate
current incidence of deflation is 1.5 percent
(ranging from 0% to 19%).
Infection
Infection is an inherent risk of any invasive
surgery, and the incidence of infection associated
with implantation of silicone gel-filled and salinefilled
mammary prostheses falls within the normal
range observed for other implant procedures.
The actual incidence rates have been reported
to range from 1 % to 9% with the vast majority
of studies reporting incidences of approximately
2% to 4%. These results are based on studies that
differ with respect to implant type, augmentation
versus reconstruction, surgical approaches,
and variations in the use of antibiotics before,
during, or after surgery. Furthermore, the studies
cover a time period of approximately 20 years.
Overall, the rate of infection appears to be lower
following augmentation for cosmetic purposes
than following augmentation after mastectomy. A
review of the literature indicates that infection is
an infrequent event following breast augmentation.
The role of infection in capsular contracture
remains speculative.
Interference with early tumour
Detection
There has been a great deal of controversy
surrounding the issue of early tumour detection
in women with breast implants. There are two
issues of concern regarding cancer detection in
these patients: 1) whether available techniques
are capable of detecting abnormalities, and 2)
whether patients are at risk for having more
advanced disease at first detection. Review of the
available studies indicates that questions remain
concerning the effectiveness of various techniques
in examining patients with breast implants. It is
difficult to draw conclusions from the studies
as they differ with respect to protocol, patient
population, types and position of implants, and
mammographic techniques. Nevertheless, there
is no conclusive evidence that silicone breast
prostheses significantly obstruct or hinder
the ability to detect breast tissue abnormalities or
breast cancer at an early stage.
The best way to alleviate the problems encountered
when examining patients with breast implants is
to employ techniques suitable for attaining the
most sensitive examination. This may involve
revised techniques of manual examination,
appropriate manipulation of the breast tissue
during mammography (i.e., Eklund technique),
obtaining additional views of the breast tissue,
and if necessary, employing additional methods
of examination such as ultrasound. Evidence also
suggests that submuscular implantation provides
for the best visualization of breast tissue during
mammography. The most important consideration
is that radiologists recognize the available methods
of examination for patients with breast implants
and that the proper techniques are employed.
It is equally important to inform patients of
the potential problems of detection, to educate
them on self-examination of their breasts, and to
encourage them to seek breast cancer screening on
a regular basis with a mammographer experienced
in dealing with breast implant patients.
Carcinogenicity
There is no evidence to suggest that silicone
gel-filled or saline-filled mammary prostheses
are associated with carcinomas in humans. There
have been several reports in the literature of breast
cancer following augmentation mammoplasty.
However, since carcinoma of the breast is likely
to affect nearly one in ten women, and it is not
uncommon to find malignancies even during the
augmentation procedure, these reports are not
unexpected.
The most convincing evidence to date for the lack
of carcinogenicity of silicone breast prostheses
comes from two epidemiological studies with
long-term follow-up in women with augmented
breasts. In a retrospective cohort study Deapen et
al. (1986), and its update by Deapen and Brody
(1992), showed no increase in breast cancer or
any other malignancies in 3,111 women with
breast implants followed for a median of 10.6
years. A population-based nonconcurrent cohortlinkage
study by Berkel et al. (1992) yielded
similar results to that of Deapen and Brody. There
was no increase in breast cancer incidence in
11,676 Canadian women who underwent breast
augmentation, with 58.1% of the cohort having
at least 10 years of follow-up. The results of these
two epidemiology studies support the finding that
silicone breast implants are not associated with an
increased risk of cancer.
Human reproductive toxicity and
Teratogenicity
Review of the literature identified a number
of studies relevant to assessing the teratogenic
potential of silicone materials. Considered
together, they provide a relatively large database
from which the teratogenic potential can be
assessed. The available data shows that silicone
materials are not teratogenic in animals.
The conclusions drawn from the animal studies
are reinforced by the published clinical literature
showing no reports of human birth defects or other
reproductive effects associated with implantation
of silicone mammary prostheses of any type.
Therefore, the weight of the evidence strongly
indicates that silicone is neither a reproductive
toxicant nor a potential human teratogen.
Immunological and/or
connective tissue disorders
Review of clinical case reports and animal
data describing cellular immunoreactivity and
immunotoxicity of silicone materials indicated
that some questions concerning the effects of these
materials on immune system function are still
unanswered. Nevertheless, there is no conclusive
evidence that silicone mammary prostheses are
causative agents in the development of connective
tissue diseases.
Case reports describing connective tissue disease
or immune related disorders among these patients
(most appearing only after the recent controversy
was made public) represent a small percentage
of the population. Not one, but a variety of
conditions have been potentially associated with
silicone breast implants. Almost all of the alleged
disorders are normally most prevalent in women
of child-bearing age, the same population that
undergoes augmentation mammoplasty. Therefore,
it is not surprising, that some cases of conditions
are reported coincidental to the presence of
breast implants. Although these reports may raise
suspicions about the immune system reactivity of
silicone, they certainly do not represent any proof
of a causal link between disease pathogenesis and
silicone.
The lack of an association between silicone
mammary prostheses and connective tissue
disorders is supported by the available animal data.
One study has shown that silicone gel can act as an
adjuvant in rats while another demonstrated that
silicone gel, even in combination with an adjuvant
did not alter lymphocytic responses or produce
host sensitization. Silicone has also been shown to
be one of the least reactive polymers when tested
for its ability to stimulate macrophage activity.
Considered together, these animal data provide
no evidence that silicone gel-filled and salinefilled
mammary prostheses should be considered
immunoreactive.
An additional dataset available for review
addressed the immunotoxicity of silicone
materials, including silicone elastomer gel and
fluid. Comprehensive testing by both the National
Toxicology Program and Dow Corning have
shown that silicone materials are not immunotoxic
and do not demonstrate immunogenicity. These
data combined with the clinical data and human
case reports suggest that implantation of silicone
breast implants does not result in immune system
responses that are consistent with any pattern of
effects related to the development of connective
tissue diseases.
Calcification
It has been suggested that calcification of the
implant capsule may interfere with tumour
detection in women with breast implants.
In the view of a leading expert in the use of
mammography in women with breast implants,
calcifications may occur within the fibrous capsule
surrounding the implant but do not compromise
the mammographic study. Such calcifications
are generally not characteristic of, or likely to
be confused with, calcifications associated with
malignancies. There are no published reports
that document any actual occurrences of missed
or delayed diagnoses attributable to capsule
calcification.
Biological effects of silica
Fumed silica is a distinct form of amorphous silica
that is used to strengthen the elastomer shells of
both silicone gel-filled and saline-filled breast
implants. As a consequence of its different physical
structure, the biological activity of amorphous
silica is significantly less than that of the crystalline
forms. For example, while it is well documented
that inhalation of crystalline silica causes Silicosis,
this toxicological effect has not been observed
following inhalation of amorphous compounds.
Although there is limited literature on the
toxicity of fumed silica following implantation
or subcutaneous administration, the available
data indicate a low degree of toxicity. Indeed,
amorphous silica has a long history of safe use
in both food and drugs. The data also show that
amorphous silica is tightly bound in the elastomer
shell, is not released from the mammary envelope
surface, and is not converted to crystalline silica
under physiological conditions.
Silicone in breast milk
Although the issue of silicone transfer into breast
milk of women with silicone gel-filled or salinefilled
breast prostheses was not raised by the U.S.
Food and Drug Administration in the 515(b)
Rules for these devices, there has been a great deal
of speculation recently on this issue. Two recently
published papers discussed the cases of several
children of women with silicone breast implants
that have developed symptoms such as arthralgias
and abdominal pain. Neither of the papers presents
data demonstrating the presence of silicone in
breast milk nor any definitive link between the
reported symptoms and the presence of silicone
breast implants in the mothers. Unpublished data
indicate that background levels of silicone are in
fact detectable in breast milk from both mothers
with and without silicone breast prostheses.
Approved over-the-counter medications for
infants also contain silicone. Therefore, based upon
the current data, silicone in breast milk should not
be considered an issue relevant to the safety of
silicone breast implants.
