An assessment of MAC 387 antibody as a diagnostically useful marker of L1 epithelial antigen expression by lung tumours.

A recent report describing the distribution of L1 epithelial antigen in lung tumours in relation to the histological type claimed that this antigen was a highly reliable marker of squamous cell carcinoma. Our study was designed to test this claim and to examine the potential of this antigen in the typing of lung tumours in biopsy specimens. A total of 143 lung tumours were typed according to the WHO classification and examined immunohistochemically for L1 epithelial antigen expression using commercially available monoclonal mouse anti-human myeloid/histiocyte antigen (MAC 387). Positivity was found in 46 of 55 squamous cell carcinomas (84 per cent), 12 of 27 adenocarcinomas (44 per cent), 15 of 16 adenosquamous carcinomas (93 per cent), 10 of 15 large cell carcinomas (67 per cent), none of 20 small cell carcinomas, and none of 10 carcinoid tumours. Of those tumours expressing L1 epithelial antigen, most showed a patchy pattern of positivity. From this study it is clear that detection of L1 epithelial antigen by MAC 387 antibody is not specific for squamous cell carcinomas, but it may have a limited use in the diagnosis of small cell carcinomas and carcinoid tumours as these are consistently negative.