Expression of the embryonal neural cell adhesion molecule N‐CAM in lung carcinoma. Diagnostic usefulness of monoclonal antibody 735 for the distinction between small cell lung cancer and non‐small cell lung cancer

Paraffin sections of 19 surgically resected small cell lung carcinomas (SCLC), 33 non-small cell lung carcinomas (NSCLC) of various types, and four bronchial carcinoids were immunostained with monoclonal antibodies (MoAbs) 735 and anti-Leu 7, both recognizing some sugar epitopes present on the neural cell adhesion molecule N-CAM. With MoAb 735, all SCLC were stained focally or diffusely, and one carcinoid was stained focally. Only three of the 33 NSCLC were faintly and focally positive with MoAb 735; these three tumours showed relatively small tumour cells and small, oval nuclei. Anti-Leu 7 stained all the carcinoids, only eight SCLC, sometimes focally, and eight NSCLC. MoAb 735 was thus superior to anti-Leu 7 in distinguishing between SCLC and NSCLE. Since MoAb 735 stained all SCLC strongly and is applicable on paraffin sections, it provides a well-needed addition to the immunomarkers used in the diagnostic distinction of SCLC and NSCLC.