BACKGROUND: Immunohistochemistry (IHC) is a valuable tool in diagnostic surgical pathology. We evaluated the frequency of IHC use and its contribution to the final diagnosis of tumors and pseudotumors. METHODS: A retrospective study of the 4,459 cases received in 1999 for immunoperoxidase study at the Immunohistochemistry Laboratory, Department of Pathology, University of Miami/Jackson Memorial Hospital, USA, was performed. RESULTS: 3,706 cases yielded all data necessary for the study. In 19% of cases IHC was used for localization of predictive tumor markers or evaluation of proliferation indicators; 17% of cases performed IHC to identify organisms or acellular structures and in 64% of cases IHC examination was to aid the pathologists in differential diagnosis of tumors. In 835 cases of the latter category, IHC helped the pathologists to render a specific diagnosis in 83% of instances. In 12% IHC narrowed down the diagnostic possibilities to two or three entities. In the remaining 5% of cases, IHC had no contribution to the final diagnosis due to limited diagnostic material, extensive necrosis or lack of tumor differentiation. The main differential diagnosis dilemmas included determination of the site of origin of carcinomas, differentiation between reactive mesothelial hyperplasia, mesothelioma and adenocarcinoma, and demonstration of cell phenotype in undifferentiated neoplasms. The average of antibodies per case was 4.1. CONCLUSIONS: Immunohistochemistry is a valuable tool in diagnostic surgical pathology capable of delineating the nature of disease in 95% of cases. In some instances, IHC is essential for the treatment decision-making. On the other hand, limited diagnostic material, extensive necrosis or lack of tumor differentiation can interfere in IHC performance. A well-designed differential diagnosis-driven utilization of the technique is extremely cost-effective.
Immunohistochemistry; Neoplasm; Carcinoma; Differential diagnosis
