Immunocytochemical characterization of large-cell carcinomas of the lung. Role, limitations and technical considerations.

To clarify the use of cytologic preparations, particularly those previously stained by the Papanicolaou method, for the immunocytochemical evaluation of large-cell carcinomas (LCCs), 37 cytologic preparations from cases diagnosed as LCC were examined using a battery of immunocytochemical stains for keratin, chromogranin, common leukocyte antigen (CLA) and B72.3. Thirty-two specimens were from the thoracopulmonary region (12 fine needle aspirates of the lung, 7 bronchial brushings, 5 bronchial washings, 2 sputa and 6 pleural fluids); the remaining specimens were fine needle aspirates of 3 lymph nodes, 1 vertebral body and 1 liver. Of the specimens analyzed, 30 of 37 were positive for keratin and 7 of 35 were positive for B72.3 (6 were positive for both). Only 1 of 37 was positive for CLA while none of 37 was positive for chromogranin. Six specimens showed no reaction with either keratin, B72.3 or chromogranin. These results confirm that the majority of LCCs consist of epithelial cells of either a squamous or an adenocarcinomatous type. They also show that immunocytochemistry is a useful diagnostic adjunct that can be applied to cytologic preparations previously stained by the Papanicolaou method; this is important since immunostaining is often considered after undifferentiated malignant cells are encountered in a previously stained preparation. However, a thorough understanding of some technical limitations is critical in the evaluation of the results of this technique when it is applied to cytologic specimens.