The goal of this clinical trial is to find out if performing a pleural fluid drainage (thoracentesis) together with the measurement of pressure inside the chest (pleural manometry) during the same procedure can help doctors choose the best treatment for each patient with malignant pleural effusion.The main questions it aims to answer are: * Is the use of pleural manometry associated with a higher success rate in managing malignant pleural effusion through pleurodesis? * Can the use of pleural manometry help guide optimal therapeutic decision-making in malignant pleural effusion? Researchers will compare the success of the chosen treatment in patients who undergo pleural manometry to those who do not, to see if pleural manometry helps improve treatment outcomes for malignant pleural effusion. Participants will: * Receive treatment according to the hospital's standard clinical practice for managing malignant pleural effusion. * If assigned to the manometry group, they will undergo pleural manometry during their first thoracentesis. * If the manometry results suggest that the lung can fully expand, they will be referred for pleurodesis-just as patients in the non-manometry group are. * If the manometry results suggest that the lung cannot fully expand, pleurodesis will not be recommended due to the high risk of failure. Instead, placement of a tunneled pleural catheter will be advised to help control symptoms.