Differential expression of antigens by human small cell lung carcinoma in sections of tumour and in serous effusions.

Antigen expression by human small cell lung carcinoma cells in serous effusions was determined by staining smears of cells with a panel of four monoclonal antibodies including UJ13A (cluster 1 antigen) and CAM 5.2 (anti-cytokeratin) using an immunoalkaline phosphatase technique. This was quantified by counting the proportion of stained and unstained tumour cells and was compared with that of small cell lung carcinoma in sections of solid tumour. Differential expression of antigen expression was noted with significantly fewer small cell carcinoma cells in serous effusions staining with UJ13A or CAM 5.2. The reasons for this differential expression are unknown, but may reflect adaptation to a different environment or be a prerequisite for spread to serous space.