Lung surfactant protein-A and carcinoembryonic antigen in pleural effusions due to lung adenocarcinoma and malignant mesothelioma

Lung surfactant protein-A (SP-A) is a major phospholipid-associated glycoprotein in surfactant, and is a useful immunohistochemical marker for lung adenocarcinoma. Carcinoembryonic antigen (CEA) has not been immunohistochemically detected in mesothelioma. In pleural effusions due to malignant mesothelioma, very low concentrations of SP-A and CEA can be expected. We studied the value of combined determinations of CEA and SP-A in pleural fluid to distinguish between lung adenocarcinoma and mesothelioma. SP-A and CEA concentrations were measured in pleural effusions from 78 patients with lung adenocarcinoma and 10 with malignant mesothelioma. SP-A concentrations in pleural effusions due to lung adenocarcinoma and mesothelioma were 516 +/- 140 and 16.9 +/- 3.6 ng.ml-1 (mean +/- SEM), respectively. CEA concentrations in pleural effusions due to lung adenocarcinoma and mesothelioma were 239 +/- 92.4 and 1.7 +/- 0.3 ng.ml-1, respectively. SP-A values did not exceed 100 ng.ml-1 in any of 10 mesotheliomas, whilst in 37 of 78 lung adenocarcinomas they did. CEA values did not exceed 10 ng.ml-1 in any of 10 mesotheliomas, whilst in 53 of 78 lung adenocarcinomas they did. Increased values of SP-A and/or CEA were found in pleural effusions from 67 of 78 lung adenocarcinomas. It is concluded that a combination of CEA and SP-A assays in pleural effusions will be helpful for discriminating lung adenocarcinoma from mesothelioma.