TGFB1 and Pleural effusion: Statistical analysis (Spearman correlation coefficient) showed no correlation between frequency of Tregs and concentration of TGF-β1 in any group of pleural effusions separately (MPEs with malignant cells: p = 0.105; MPEs without malignant cells: p = 0.0598; nMPEs: p = 0.369) (Figure 6(a)).