<h4>Objectives</h4>The objectives of this study included assessing the diagnostic performance of HE4 in malignant pleural effusions (MPEs) and identifying the benign etiologies associated with higher HE4 concentrations.<h4>Methods</h4>The study involved patients with pleural effusion (PE) treated at Part Taulí University Hospital. The gene discussed is WFDC2; the disease is Pleural effusion.