Immunoreactivity for LN2 and LN3 distinguishes small cell carcinomas from non-small cell carcinomas in the lung

Immunoreactivity to LN2 and LN3, monoclonal antibodies that recognize compo nents of the class II major histocompatibility complex, was assessed in 72 cases of non-small cell lung carcinoma (NSCLC) (32 biopsy specimens, 40 res ection specimens) and 64 cases of small cell carcinoma (56 biopsy specimens , 8 resections) of the lung All cases were reviewed independently by three pathologists for histological classification. Only I of the 64 small cell c arcinomas showed immunoreactivity for LN2, and none of the 64 cases showed reactivity for LN3. Among the non-small cell carcinomas, 25 of 48 cases wer e positive for LN2 and 43 of 71 were positive for LN3; the sensitivity was greater for adenocarcinoma (78.5%) than for squamous cell carcinoma (37%). A combined sensitivity of 64.7% was observed when the results of LN2 and LN 3 were combined, and this sensitivity was not significantly diminished in t he biopsy subset of cases (59.4%). Differentiation within histological subt ypes of NSCLC tie, well, moderate, or poorly differentiated) did not alter test sensitivity. In conclusion, LN2 and LN3, used alone or in combination, appear highly specific for non-small cell carcinoma and moderately sensiti ve in both biopsy and resection specimens; therefore, these antibodies may be diagnostically useful in distinguishing small cell from non-small cell c arcinoma of the lung. HUM PATHOL 29:1441-1446. Copyright (C) 1998 by W.B. S aunders Company.