الفهرس 
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Abstract
The purpose of the present study was to demonstrate the expression me! distribution of cyclin D I protein in oral squamous cell carcinoma.
Thirty-seven specimens of oral squamous cell carcinoma of different ~rades of di fferentiation were collected as fresh specimens and paraffin olock. Paraffin blocks were cut into sections of 4~lm. some section were ~rocessed for routine haematoxylin and eosin stain for confirmation of the uiagnosis while, the other sections were processed for the demonstration of eyclin D I by the streptavidin·-biotin immunoperoxidase technique following Ihe manufacturer’s instructions.
Normal oral mucosa adjacent to squamous cell carCllloma tissue ~howed cyclin D I immunoreaction as a mild to moderate reaction limited to prickle cell layers in the superficial part of surface epithelium.
In hyperplastic epithelium, adjacent to tumor tissue there was a moderate cyclin D 1 imm uno-reactions in most of the suprabasal cells and occasional positive reaction in some basal cells.
In dysplasia, adjacent to tumor tissue there was increase in the positivity of cyclin D 1 immunoreactions with the increase in the degrees of dysplasia fTom focal atypia to sever dysplasia. The positive reaction was detected in both basal and suprabasal cells.
In squamous cell carcinoma, cyclin Dl was variably detected .In wellldifferentiated squamous cell carcinoma, cyclin Dl reaction positive reaction was detected within the epithelial masses as well as in the peripheral cells of
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keratin pearls. While, cyclinDl negative reaction was detected in the keratin substances. In moderately differentiated squamous cell carcinoma, there was increase in the cyclin 0 I positive reaction of almost all epithelial cells within the cell nests .In poorly differentiated squamous cell carcinoma, (here was intense positive cyclin D I immunoreaction in all anaplastic cells within the irregularly formed tumor masses.
from the results of this work, it IS concluded that there was a significant correlation between the cyclin D I protein expression and the degree of differentiation of tumor cells wherease, there was a down regulation of cyclin D I protein expression up on differentiation.