Cytotoxic Natural Killer Subpopulations As a Prognostic Factor of Malignant Pleural Effusion

Background: Malignant pleural effusion (MPE) is a sign of advanced disease of poor prognosis. As natural killer (NK) cells are involved in the first line of tumour defence, we aimed to validate a new diagnostic and prognostic indicator for MPE based on NK subpopulations of pleural fluid (PF) and peripheral blood (PB).

Methods: NK subpopulations were determined in PF and PB in 71 patients with malignant, paramalignant or benign pleural effusion. The receiver operating characteristic (ROC) curves, Kaplan-Meier, multivariable Cox model and decision trees created with the CHAID (Chi-square automatic interaction detector) methodology were employed.

Results: We demonstrated that the PF/PB ratios of the CD56 bright CD16- and CD56 dim CD16- NK subpopulations were higher (p = 0.013 and p = 0.003, respectively) in MPEs and paramalignant pleural effusions (PPEs) than in benign ones, with an AUC of 0.757 and 0.741, respectively. The PF/PB ratio of CD16+ NK and CD57+ NK obtained a higher hazard ratio (HR) in the crude Cox's regression analysis. In the adjusted Cox's regression analysis, the PF/PB ratio of CD16+ NK gave the highest HR (HR 6.1 [1.76-21.1]) (p = 0.004). In the decision tree created for the MPE prognosis, we observed that the main predictor variable among the studied clinical, radiological, and analytical variables was lung mass, and that 92.9% of the patients who survived had a PF/PB ratio of the CD56 dim CD16+ NK subpopulation ≤ 0.43.

Conclusions: Our data suggest that both the PF/PB ratios of cytotoxic subpopulations CD57+ NK and CD16+ NK are useful as a prognostic factor of MPE. Other subpopulations (CD56 bright CD16- and CD56 dim CD16- NK) could help to diagnose MPE.