Expression of the small cell carcinoma antigens of cluster-5 and cluster-5A in primary lung tumours.

The expression of the small cell carcinoma (SCLC) antigens cluster-5 (antibody LAM8) and cluster-5A (antibody SWA20) was examined on a panel of routinely processed biopsy or surgical specimens of 290 lung tumours by immunoperoxidase staining. Antigen expression was largely restricted to SCLC. Of over 150 tissue samples evaluated, moderate or strong antigen expression was found in 49% (cluster-5) and 45% (cluster-5A). Concordance in expression of the two antigens was seen in 71% of SCLC samples, with 35% expressing both antigens strongly, 8% moderately and 28% being negative for both antigens. Antigen expression was independent of the morphological subtype of SCLC. Primary lung tumours of other histology, including squamous cell carcinoma, large cell carcinoma, adenocarcinoma, mesothelioma or carcinoid had no significant antigen expression. Of 135 tumours, strong or moderate expression of both antigens was seen only in two cases. 20%, mostly carcinoids, were weakly positive for cluster 5 and 4% for cluster 5A antigen. The remainder were antigen negative. No significant antigen expression was seen in 25 normal lung tissues. The membrane antigens of SCLC cluster 5 and 5A are markers for SCLC and their expression in tissues is tumour-associated.