METHODS
Bcl-2 and p53 expressions were determined by immunohistochemistry in 100 oral mucosal biopsies
including NOM (n=20), OLP (n=40) and OSCC (n=40).
RESULTS
There were no significant differences in p53 and bcl-2 expressions between OLP and OSCC cases. However,
p53 expression was higher in OLP and OSCC compared to normal epithelium (p<0.05).
CONCLUSION
The results of this study suggest that changes in proteins responsible for cell proliferation and apoptosis
may play a role in the possible malignant transformation of OLP, but other molecular mechanisms involved
in the cell cycle may also have an impact on the development of oral carcinogenesis. Therefore,
long-term follow-up of patients with OLP with an accurate final diagnosis to be made by clinicopathological
correlation, further research is needed to identify markers and independent risk factors that
predict malignant transformation of OLP.
Keywords: bcl-2; malignant transformation; p53; oral lichen planus; oral squamous cell carcinoma
The incidence of oral LP (OLP) differs from country
to country; the rates reported in studies are 0.3%
in Malaysia, 0.5% in Japan, 1.15% in Turkey, 1.9% in
Sweden, and 2.6% in India.[
The exact etiology of LP is unknown. Studies support
its etiopathogenesis that it is a T cell-mediated
autoimmune disease in which autocytotoxic CD8+ T
cells cause apoptosis in cells in the basal layer of the
oral mucosa. The response of T cells causes local inflammation.[
The histopathological examination of OLP reveals
band-like lymphocytic infiltration in contact with the
epithelium in the lamina propria and liquefaction degeneration
in the keratinocytes in the basal layer. There
is no dysplasia of the epithelium.[
Diagnosis of OLP is based on a combination of
clinical and histopathological criteria.[
It has been reported by various authors that oral
squamous cell carcinoma (OSCC) can develop from
OLP. The World Health Organization (WHO) has
also defined OLP among precancerous lesions since
2005. According to this classification, OLP is one of
the clinical conditions associated with a significantly
increased risk for OSCC.[
OSCC is a malignant neoplasm of stratified squamous
epithelium originating from the mucosal epithelium.
It is most common in the fifth and sixth
decades of life. Risk factors such as smoking, smokeless
tobacco use, and alcohol consumption play a role
in the occurrence of OSCC in various geographies
related to daily life habits. Worldwide, OSCC is more
common in men than women. However, concerning
the daily usage habits of risk factors, it is more common
among women in some geographical regions
such as India and Thailand. In general, OSCC occurs
during advanced age, with most patients aged 50-70
years. Depending on the tobacco use habits that vary
from country to country, the incidence or age of occurrence
has lowered.[
The growth of keratinocytes is regulated by the balance
between molecules such as bcl-2, which controls
cell survival, and p53, which controls cell death.[
Among many proteins involved in cell proliferation
and apoptosis processes, p53 and bcl-2 are also
involved in the carcinogenesis process as well as these
functions.[
This study aimed to evaluate the expression of p53
and bcl-2 proteins in OLP and compare it with normal
oral mucosa (NOM) and OSCC to obtain information
about the malignant transformation potential of OLP.
Immunohistochemistry
Immunohistochemical reactions against bcl-2 ready
to use (Thermo Scientific, Mouse, Monoclonal MS-
123-R7) and p53 (ScyTek Lab., A00009, ready to use,
Logan, Utah, USA) were performed in 5 µm thick sections
on charged slides. They were deparaffinized with
xylene for 30 min and washed with 99% alcohol for 15
min, then 96% alcohol and distilled water. For antigen
retrieval, the sections were microwaved 4 times for 5
min in citrate buffer (Ph 6.0), cooled to room temperature
and then washed in phosphate-buffered saline
(PBS) for 5 min. Endogenous peroxidase activity was
blocked by incubating the sections with 3% H2O2 and
they are washed in distilled water and waited in PBS for
5 min. To prevent non-specific reactions, sections were
incubated with block solution. Slides were incubated
for 120 min with bcl-2 and p53. Negative control sections
treated with phosphate-buffered antibodies were
confirmed to be unstained. The secondary antibody
was reacted for 25 min, followed by a streptavidin peroxidase
reagent for 25 min. AEC (ScyTek Lab., ACJ125,
Logan, Utah, USA) chromogen was used to visualize
the reaction. Finally, the sections were counterstained
with Mayer's hematoxylin, cover-slipped, and evaluated
by a light microscope.
Evaluation Methods
Cases were assigned to one of the following categories:
0% positive cells (-), <10% positive cells (+), 10-
25% positive cells (++), 26-50% positive cells (+++), or
>50% positive cells (++++).
All calculations were performed by the SPSS 11.0
(Statistical Package for the Social Science). The student's
t-test was performed, and p<0.05 was considered
to be statistically significant.
Samples were examined at 400× in Olympus BX60 microscope
attached to a color video camera (Olympus
Analysis Five) which was connected to a computer. Images were captured using the camera and displayed
on a computer monitor for evaluation. The expression
index was determined based on the percentage of positive-
stained cells in basal and parabasal layers in five
high power fields. Samples were scored semi-quantitatively
by developing the grading system applied by
Tronstad et al.[
Bcl-2 expression was observed especially in the basal layer of epithelium in OLP and normal oral mucosa groups and peripheral areas of islands of OSCC cases. No statistically difference was observed among groups in terms of bcl-2 expression (p>0.05).
Regarding p53 expression, there were no significant differences between OLP and OSCC groups (p>0.05). However, p53 expression was higher in OLP and OSCC when compared to the normal oral epithelium (p<0.05).
Figures
OLP: Oral Lichen Planus; OSCC: Oral Squamous Cell Carcinoma; NOM: Normal Oral Mucosa.
OLP: Oral Lichen Planus; OSCC: Oral Squamous Cell Carcinoma; NOM: Normal Oral Mucosa.
At present, there is no single marker that can predict
the malignant transformation of OLP. As is known, progression
from this specific OPMD to OSCC requires a
multistep process in which several genetic events occur
that trigger DNA modifications along with epigenetic
events. OLP is more likely than normal epithelium to
undergo malignant transformation because of chronic
T-cell-mediated damage to the epithelium.[
The lymphocytic infiltrate in OLP consists almost
entirely of T cells. This infiltrate is consisting of predominant
in CD4+ helper cells and fewer cytotoxic CD8+ T
cells.[
Some of the studies[
In this study, p53 and bcl-2 expression was found to
be higher in the OLP group and OSCC group than in
the NOM group. No statistically significant difference
was observed between OLP and OSCC of p53 and bcl-
2 expression.
Similarly, de Sousa et al.[28] reported that no statistically
significant difference was observed between
OLP and OSCC of p53, bax, and bcl-2 expression in
their study. The results of this study show that there was
a change in the expression of important proteins related
to apoptosis regulatory mechanisms, creating a suitable
environment for malignant transformation. Therefore,
they suggested that the findings may be evidence of the
malignant transformation potential of OLP.
According to de Sousa et al.[
p53 overexpression in OLP is mostly associated
with the wild-type form, which arrests the cell cycle for
DNA repair or induction of apoptosis.[
Unlike de Sousa et al.,[
Malignant transformation occurs less frequently
than expected and when there is a defect in the TP53
system, as p53, which is highly activated in epithelial
cells, directs the repair or apoptosis of damaged DNA
by arresting the cell cycle for DNA repair. In heavily
attacked, proliferating cells that do not undergo apoptosis
and are not controlled by p53, the accumulation of mutagenic events can lead to the development of a
malignant phenotype.[
p53 expression results of this study indicate that the
escape mechanism of tumorigenesis is reduced in these
lesions, thus increasing the risk of developing OSCC.
On the other hand, it has been suggested that malignant
transformation may occur with the malfunction
of the p53 system, which is activated in epithelial cells
and stops the cell cycle for DNA repair. In clinically
riskier (erosive/atrophic) cases, a cut-off value for p53
expression should be established, and cases with a
strong possibility of malignant transformation should
be determined and followed more closely.
Apoptosis is a programmed cell death induced by
cell damage. It is not known who initiated the apoptosis
in OLP, but the damage caused by T cells in basal
layer cells is thought to be the factor that initiated the
apoptosis. Research has shown that the rate of proliferation
in epithelial cells increases due to the damage of
T cells in OLP.[
In this study, a similar immunoreaction with bcl-2
was observed in NOM, OLP and OSCC groups, and
there was no statistical significance between them.
Likewise, Bloor et al.[
Some studies[
Accumulation of mutagenic events can lead to the
development of a malignant phenotype unless lymbyphocytic intensely attacked proliferating cells undergo
apoptosis and are controlled by p53.[
The bcl-2 findings of this study suggested that the absence
of apoptosis in OLP may be related to a mechanism
that protects the epithelium, or that the expression of bcl-
2 is not an indicator of malignant transformation of OLP.
The findings of this study suggest that other molecules
involved in cell cycle arrest, DNA repair and
apoptosis processes may play a role in the possible
transformation of OLP to OSCC.
Although numerous studies have been conducted
on various proteins involved in cell proliferation and
apoptosis processes in OLP, it is unclear whether there
is an independent risk factor for malignant transformation.
In many studies on malignant transformation
of OLP, secondary risk factors such as tobacco and alcohol
use, which are important etiological factors for
OSCC, have not been evaluated. Data from most studies
on the premalignant potential of OLP are different
and inconsistent.[
Fitzpatrick et al.[
Therefore, diagnosing OLP should be cautious. The
malignant potential of OLP is still controversial due to
the lack of consensus on the correct diagnostic criteria.
The diagnosis of OLP is made by clinicopathological
correlation. It is known that in some cases, the diagnosis
of OLP is made only by clinical findings.[
Diagnostic criteria standard, risks, predictive markers,
and cut-off values for these markers should be defined
for malignant transformation of OLP.
Acknowlegement: The author would like to thank Merve Çiçek and Mehmet Bozoğlu for their valuable help in laboratory procedures, Dr. Alper Sinanoğlu for their careful clinical diagnosis and evaluation, and Dr. Merva Soluk Tekkeşin and Dr. Vakur Olgaç for their unique contributions.
Peer-review: Externally peer-reviewed.
Conflict of Interest: All authors declared no conflict of interest.
Ethics Committee Approval: The study was approved by the Istanbul University Ethics Committee (No: 751/14, Date: 28/04/2014).
Financial Support: None declared.