Water coming out from inside the chest cavity of lung cancer may be caused by metastasis of lung cancer, or it may be caused by hypoproteinemia, obstructive pneumonia and other diseases. 1. Lung cancer metastasis:Lung cancer metastasis may occur when the condition of lung cancer patients deteriorates. When lung cancer metastasizes to the pleura, it may cause the pleura to secrete a large amount of exudate to the patient’s chest cavity, and pleural fluid will appear, so lung cancer patients will have the phenomenon of water coming out from inside the chest cavity. 2. Hypoproteinemia:If lung cancer patient enters the advanced stage, the patient will have the symptom of loss of appetite, which leads to malnutrition. At this time, the protein concentration in the patient’s blood will be lowered, which will cause the colloid osmotic pressure of the patient’s blood to decrease, thus leading to the water in the patient’s blood seeping into the pleural cavity to form effusion. Therefore, lung cancer patients have the symptom of water coming out of chest cavity. 3. Obstructive Pneumonia:As lung cancer patients have tumors in lungs, the tumors will obstruct the lungs and obstructive pneumonia will appear. The patient will be infected, which will stimulate the pleura to secrete exudate, so the lung cancer patient will have the symptom of water coming out of chest cavity. When lung cancer patients have the symptom of water coming out of chest cavity, they should consult doctor in time to find out the cause and follow the doctor’s instruction for treatment.