The application of immunocytochemical techniques to routinely-fixed and stained cytologic specimens. An aid in the differential diagnosis of undifferentiated malignant neoplasms.

Routinely-fixed and Papanicolaou stained smears with the cytologic diagnosis of undifferentiated malignant neoplasm that had been prepared with cells obtained by fine needle aspiration biopsy (n = 7), pulmonary lavage (n = 5), or thoracentesis (n = 3) from 15 unselected patients were stained by an immunocytochemical technique to evaluate the presence of keratin proteins and the leukocyte common antigen (LCA). Commercially available, well-characterized monoclonal antibodies with specificities for keratin proteins and the leukocyte common antigen, and a streptavidin-biotin-horseradish peroxidase labelling method were used. Evaluation of the stained smears revealed the presence of one of the two antigens in material obtained from each patient, thus indicating the probable cell-lineage of the neoplastic cells. The specificity of the monoclonal antibody reagents used was further evaluated in routinely-fixed and stained cytologic material from 24 histologically confirmed carcinomas and 12 lymphomas. In conclusion, immunocytochemical techniques may be successfully applied to routinely processed archival cytologic smears to determine the antigenic profile of morphologically undifferentiated cells and therefore aid in the differential diagnosis of undifferentiated malignant neoplasms.