Elevated pleural fluid RCAS1 is a diagnostic marker and outcome predictor in lung cancer patients.

RCAS1, a type II membrane protein also secreted in soluble form, may be important in tumor cell evasion of immune surveillance and contribute to the aggressiveness of human tumors. We examined the implications of elevated pleural fluid RCAS1 at the onset of effusion in lung cancer patients. Of 102 patients presenting with pleural effusion, 59 proved to have a malignant effusion and 43, nonmalignant. Malignant effusions exhibited higher RCAS1 concentrations than nonmalignant effusions (mean +/- SD; 36.3 +/- 114 vs. 2.7 +/- 1.8 U/ml; p=0.014). Lung cancer patients with pleural fluid RCAS1 concentrations below 15 U/ml had a longer mean survival than those with higher concentrations (4.7 vs. 1.7 months; p<0.05). By multivariate analysis, pleural fluid RCAS1 was an independent prognostic factor in lung cancer patients with effusion. In conclusion, RCAS1 determination at onset of pleural effusion is informative for both diagnosis and outcome prediction in lung cancer patients.