To characterize levels of soluble HMGB1 in pleural effusions from malignant and benign etiologies, an HMGB1-specific ELISA was performed on the acellular fraction of pleural effusions from patients with metastatic MPE (N = 46) or benign pleural effusion (BPE) (N = 24). This evidence concerns the gene HMGB1 and Pleural effusion.