الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
Oral squamous cell carcinoma is the most common malignant tumor in
the oral and maxillofacial region. The worse prognosis of OSCC is attributed
to the fact that a significant lesion is not diagnosed or treated until it reaches
an advanced stage.
Tobacco smoking is a well known oral carcinogen that plays an
important role in the high incidence of oral cancer. Enzymatic bioactivation of
pro-carcinogens present in tobacco contributes to DNA damage and
genotoxicity. DNA repair genes are responsible for correction of any damage
occuring along the structure of the DNA. O6-methylguanine-DNA
methyltransferase (MGMT) is a specific DNA direct reversal repair protein
that removes mutagenic, carcinogenic, and cytotoxic adducts from O6-
methylguanine lesions in DNA. The process of direct repair is completely
error-free, granting a major advantage in preservation of genetic information.
The aim of the present work is to study the possible difference in the
cellular expression of the DNA repair MGMT in case of Squamous cell
carcinoma in smoker and non-smoker patients.
Twenty two cases of OSCC biopsies were included in the present
study. Biopsies were histologically evaluated using H&E staining .The
microscopical examination showed that out of the 22 cases, 8 (36.8%) were of
the well differentiated type, 12 (54.5%) were moderately differentiated OSCC
and 2 (9.1%) were poorly differentiated. The 22 cases were divided equally
into 2 groups, one is smoker and the other is non-smoker.
Serial sections were immunohistochemically stained by monoclonal
antibody to MGMT using Labeled- Strept -Avidin Biotin complex method
(LSAB). The intensity of immunostaining of MGMT was calculated in terms
of mean area percent and mean optical density by the computer image
analyzer.
All the non smoker OSCC cases showed positive brownish
immunoexpression. The immunoreaction was seen in the cytoplasm as well as
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the nuclei of the malignant epithelial cells. Most of the OSCC smokers group
showed negative immnunoreactivity to MGMT. However 3 cases revealed a
weak positive immunostaining with only sporadic cells at the periphery.
The mean area percent and the mean optical density of MGMT in
OSCC biopsies were calculated and correlated to the smoking habit. A high
significant statistical difference (p <0.001) was found between the smoker and
non-smoker OSCC patients. In the non-smoker group there was no significant
difference between patients who never smoked and ex- smoker patients who
ceased the habit 10 years ago or more. Also in the smoker group no
significant difference was observed in relation to the duration as well as the
intensity of the smoking habit.
This study concluded that MGMT protein was detected in all the nonsmoker
cases of OSCC and in a small percentage of the smoker patients.
Therefore it is reasonable to support that continuous exposure to smoking
may inhibit the function of that DNA repair enzyme. MGMT detection may
have potential prognostic and predictive values in the management of OSCC
cases. Further studies are needed to clarify any positive relation between
MGMT immunoexpression and the different histological grades of OSCC,
also to evaluate the therapeutic effect of DNA repair genes as an outlet in
cancer therapy.