Immunocytologic diagnosis of small-cell lung cancer in imprint smears

Imprints of histologic or autopsy specimens from 12 small-cell lung cancers (SCLCs), 82 non-SCLCs (50 adenocarcinomas, 25 squamous-cell carcinomas, 1 adenosquamous carcinoma and 6 large-cell carcinomas), 2 carcinoid tumors, 1 malignant lymphoma and 8 metastatic carcinomas were examined immunocytologically for the presence of cluster 1 SCLC antigen (neural-cell adhesion molecule: N-CAM), chromogranin A, Leu-7, neuron-specific enolase (NSE) and gastrin-releasing peptide (GRP). The monoclonal antibodies NCC-LU-243 and NCC-LU-246, which are reactive with cluster 1 SCLC antigen/N-CAM, diffusely stained the cell membranes of all SCLCs and carcinoid tumors (100%) and diffusely and focally stained those of two of the large-cell carcinomas, two of the adenocarcinomas, two of the squamous-cell carcinomas and the one adenosquamous carcinoma. Malignant lymphoma and metastatic carcinoma were negative for this antigen. A few cases of large-cell carcinoma, adenocarcinoma, squamous-cell carcinoma and adenosquamous carcinoma were also stained with these antibodies, which may indicate a neuroendocrine differentiation. However, these tumors were different from SCLCs in that their positive tumor cell population was definitely smaller than that in SCLC, in which almost all tumor cells were positive. This confirmed the usefulness of antibodies against cluster 1 SCLC antigen for the immunocytologic diagnosis of SCLC and carcinoid tumor in imprint smears. Chromogranin A, GRP, NSE and Leu-7 were not useful in immunocytologically differentiating the imprints from these cases since only a few tumor cells were reactive with these antibodies. The antibodies against cluster 1 SCLC antigen/N-CAM can also be applied to cytologic preparations of sputum, pleural fluid and fine needle aspirates stained routinely by the Papanicolaou method since the antigen is preserved in such alcohol-fixed smears.