"The Role of Cancer Immunohistochemistry" TUMOR TIDBITS, A BIWEEKLY EMAIL NEWSLETTER FROM GULF COAST VETERINARY ONCOLOGY Number 86; January 31, 2003. ======================================================================= THIS WEEK'S TUMOR TIDBIT: The Role of Cancer Immunohistochemistry ======================================================================= ANNOUNCEMENTS Second Annual Patient Celebration -- Three days of service in San Antonio -- New clinical trials. Check our web site or call us for additional details. ======================================================================= This Tidbit discusses some of the interesting features of immunohistochemistry in cancer medicine. The identification of neoplastic disease relies on the microscopic features of the tumor cells and their similarity to normal cellular counterparts. Thus ,in cases of well differentiated tumors cellular identify is frequently achieved. However, poorly differentiated or blastic tumors assigning a cell of origin becomes much more difficult. It is in these specific cases that the detection of cellular antigens can provide critical information as to the possible origin of the tumor cells. Historically, the determination of enzyme activity has been used in cases lymphoma and leukemia in fresh samples. Enzyme testing in paraffin sections was less than ideal due to the formalin fixation artifacts. However, by using antibodies toward cellular antigens, immunocytochemistry and immunohistochemistry are able to identify a large number of proteins which can assist in determining the cells of origin of many normal and neoplastic cells. The basic technique relies on the formation of an antibody-antigen complex on a solid matrix, very similar to an ELISA assay. The final product is a colored precipitate deposited on the cells upon which the antibody-antigen complex was formed. Thus specific antigens can be detected and identified with specific cells within the smear or paraffin section. There are hundreds of antibodies used for immunohistochemical tests by laboratories at various state and private centers. Some are quite specific, meaning that they react only with one type of cancer. Others may react with a few types of cancer, so testing with several antibodies makes a decision about a cancers origin. By considering these results in the context of the cancer's appearance after routine processing, the location of its metastasis, and other information about the patient (age, gender, etc.), it is often possible to find the source of the cancer or to classify the cancer in a way that can help guide treatment. Anaplastic or undifferentiated tumors represent a diagnostic challenge. Identification of the tissue of origin of an undifferentiated tumor is important in determining prognosis and planning treatment. Immunohistochemistry, using either monoclonal or polyclonal antibodies, can be helpful when the tissue of origin of a tumor cannot be determined with standard stains. Various characteristic cytoplasmic markers in normal tissues, when identified in undifferentiated neoplastic tissue, help to determine origin. The presence or absence of intermediate filaments is one of the more important classes of tumor markers. Intermediate filaments are filamentous proteins that are ultrastructurally recognizable as straight or slightly curved filaments 8 to 10 nm in diameter. They are intermediate in size between two other cytoskeletal structures: the microfilaments that are approximately 6 nm in diameter and composed of actin, and the microtubules that are about 25 nm in diameter. Large families of intermediate filaments, known as cytokeratin filaments, are typical of epithelial cells and carcinomas. Nineteen subclasses of cytokeratin filaments, ranging from 40 to 68 kilodaltons, have been identified with monoclonal antibodies. Epithelial tissue and tumors of epithelial origin (carcinomas) stain positive for various cytokeratin filaments with the appropriate monoclonal antibody and standard immunohistochemical techniques such as the avidin-biotin-peroxidase complex method. Distinct intermediate filaments are found in other tissues and are useful in identifying undifferentiated tumors. Glial fibrillary acidic protein is present in glial cells and gliomas. Neural filaments are diagnostic of neural cells and some types of neuroendocrine tumors. Vimentin is an intermediate filament that is typical of mesenchymal cells and their derived tumors such as melanomas and other nonepithelial neoplasms. Desmin is an intermediate filament that is characteristically present in muscle cells and in most tumors derived from muscle cells. Kappa and lambda light chains are excellent markers for detecting canine B-cell lymphomas and plasmacytomas. Neuron-specific enolase and S-100 protein are often present within amelanotic melanomas. The combined use of vimentin, S-100 protein, and neuron-specific enolase is useful in distinguishing amelanotic melanoma from other undifferentiated round cell tumors in dogs. CD18 can be used to detect all bone marrow derived cells, while CD3 will stain T-cells and CD79a will mark B-cells. Myeloid cells can be identified by their positive staining for Calprotectin, express only by cells of the myeloid lineage. Other connective sarcomas can also be determined through the used of Smooth Muscle Actin, Desmin, Factor VIII and GFAP , to mention a few. While carcinomas can also be further characterized by staining for specific proteins such as various hormones and hormones receptors such as Estrogen Receptor. SO WHAT DO WE DO AT GULF COAST? * When presented with a patient having an undifferentiated malignancy, a "malignant round cell tumor", or a suspect amelanotic oral malignancy, the first thing we do is call the pathologist listed on the histology report. Nothing helps the pathologist more than a thorough history and clinical review of the patient in deciding upon the tissue of origin and the appropriate histological interpretation. * When the routine histologic review is still uncertain, we consult with the pathologist regarding the use of appropriate immunohistologic methods to arrive at a final diagnosis. * With most referral pathology laboratories, the additional time and cost is minimal and the information can be critical to arriving at an appropriate prognosis and therapy plan for the patient. ======================================================================= As always, we hope this info helps and don't hesitate to call or email us Gulf Coast Veterinary Oncology! Kevin A. Hahn, DVM, Phd, Diplomate ACVIM (Oncology), drhahn@gcvs.com Janet K. Carreras, VMD, Diplomate ACVIM (Oncology), drcarreras@gcvs.com Glen K. King, DVM, MS, Diplomate ACVR (Radiology & Radiation Therapy), drking@gcvs.com Gulf Coast Veterinary Diagnostic Imaging & Oncology 1111 West Loop South, Suite 150, Houston, TX 77027 P: 713.693.1166 F: 713.693.1167 W: www.gcvs.com