Advances and New Concepts in Oral and Maxillofacial Pathology

Abstract

Improvement in the treatment of patients has come through new surgical techniques, improved modalities of therapy, and better understanding of disease processes. The role of the pathologist is to elucidate and clarify the pathogenesis of disease. For many years, advances in the understanding of neoplastic disease have been achieved by pathologists through the recognition and classification of tumors via standard light microscopy using routine hematoxylin and eosin staining, occasionally complemented by specific histochemical stains. The advent of electron microscopy yielded further morphologic information but was limited in application by its expense, the size of the operating unit, and the requirement of fresh tissue. Over the past 2 decades, further characterization of tumors became feasible using newly developed diagnostic techniques. In addition, the ease of obtaining tissue samples has been enhanced by new approaches such as fine-needle aspiration biopsy. Analysis of the molecular characteristics of certain tumors has become the standard of care, contributing to more specific classification and treatment recommendations. Recent molecular biologic advances have made such analyses not only possible but relatively convenient. Labeled probes have been developed that help to analyze nucleic acid sequences. Techniques used to identify and quantify the nucleic acid content of cells include filter hybridization (dot blot, Southern blot, Northern blot, etc.), DNA or RNA in-situ hybridization, quantification of argyrophilic nucleolar organizer regions (AgNOR), and flow cytometric analysis. Cellular proteins other than nucleic acids can be recognized by immunohistochemistry and Western blot techniques. The use of polymerase chain reaction (PCR) has added to the efficacy of many of these techniques by providing a means of nucleic-acid amplification during testing. This technique allows the amplification of small quantities of nucleic acid (body fluid, peripheral white cells, aspirates, cytology, etc.). It is critical to distinguish among various types of tumors, because treatment is often determined by tumor type. For example, it is no longer acceptable to rely on clinical and microscopic evaluation alone to determine if a malignant round-cell tumor represents a leukemic infiltrate, lymphoma, neuroblastoma, rhabdomyosarcoma, or poorly differentiated carcinoma. Instead, immunohistochemical markers are used to help distinguish whether the tissue of origin is epithelial, neurogenic, myogenic, lymphoid, or metastatic. DNA and RNA in-situ hybridization are available to identify intracellular pathogens. AgNOR and flow cytometric analysis are used to evaluate cell kinetics in an attempt to predict biologic behavior of tumors and patient response to treatment. The focus of this discussion is not meant to be inclusive of all of the most recent diagnostic techniques currently available, but it presents an overview of the most commonly applied new approaches to diagnosis.