PROM1 and metastatic malignant neoplasm in the lymph nodes: ROC - receiver operating characteristic. HIF-1α - hypoxia-inducible factor-1α. CD133 - prominin-1. P - pleural fluid concentration. S - serum concentration. LNM - lymph node metastasis. MPE - malignant pleural effusion. AUC - area under the receiver operating characteristic curve. CI - confidence interval. PPV - positive predictive value. NPV - negative predictive value. The cut-offs for HIF-1α and CD 133/HIF-1α (S) ratio were chosen according to Youden index. P < 0.05 was considered statistically significant.