EXPRESSION OF ARGYROPHILIC NUCLEOLAR ORGANIZING REGION COUNTS AND PROLIFERATING CELL NUCLEAR ANTIGEN IN EPITHELIAL ODONTOGENIC TUMORS

INTRODUCTION: Odontogenic tumors are diverse groups of lesions derived from odontogenic tissues. Clinical behavior of these lesions varies widely, ranging from benign to malignant with differences in recurrence rate and growth pattern. A better understanding of the underlying molecular mechanisms will help to predict the course of odontogenic tumors and lead to the development of new therapeutic applications. Nucleolar organizer regions (NORs) are loops of DNA that codify the ribosomal RNA and are considered important for protein synthesis. The NORs stained histochemicaly by silver are named argyrophilic nucleolar organizer regions (AgNOR). Quantification of AgNOR represents a valuable parameter of cell kinetics and therefore cell proliferation. The number of AgNOR sites in malignant cells is significantly greater than those in their normal or benign counterparts. Proliferating cell nuclear antigen (PCNA) is a useful marker of cellular proliferation and DNA replication. Malignant tissue is characterized by an uncoordinated proliferating cell nuclear antigen (PCNA). OBJECTIVES: To evaluate the cell proliferation rate using the expression of Argyrophilic Organizing Region counts and Proliferating Cell Nuclear Antigen in epithelial odontogenic tumors and to assess the usefulness of AgNOR and PCNA as markers in malignant potential of epithelial odontogenic tumors. MATERIALS AND METHODS: This study was done on 45 surgical specimens of epithelial odontogenic tumors and one control specimen from normal tooth germ.The tissue biopsies were processed and paraffin sections were prepared. Hematoxylin and eosin-stained sections were examined for diagnosis. Other sections were subjected to AgNORhistochemical technique and immunohistochemical staining for PCNA. Immunohistochemical staining was performed using a Labeled Strept-Avidin Biotin complex method (LSAB). RESULTS: The mean AgNOR count of tooth germ was 1.21 and the benign odontogenic tumors was 1.862.The highest AgNOR count was recorded in Ameloblastic carcinoma and lowest was seen in adenomatoid odontogenic tumor. Statistically significant difference in AgNOR counts of ameloblastoma and adenomatoid odontogenic tumor, ameloblastoma and calcifying epithelial odontogenic tumor, benign odontogenic tumors and ameloblastic carcinoma were seen. AgNORs in ameloblastic carcinoma were more in number and more widely distributed.The highest mean value of PCNA-positive cell percentage was demonstrated in ameloblastic carcinoma followed by ameloblastoma. A significant difference was noted when the PCNA value of ameloblastoma was compared with that of ameloblastic carcinoma. CONCLUSIONS: AgNOR technique may be considered a good indicator of cell proliferation in epithelial odontogenic tumors.The PCNA expression, along with the clinical features, can predict the aggressiveness, chances of recurrence and malignant potential of these tumors.