Cancerous pleural effusion is also called malignant pleural effusion. About 1/3 or more are caused by lung cancer, other tumors such as breast cancer, lymphoma and many other tumors can metastasize to the pleural cavity and cause cancerous pleural effusion, and 5%-10% of malignant pleural effusion cannot find the primary focus. Cancerous pleural fluid is a manifestation of tumor spreading to the pleural cavity, which indicates that the tumor is advanced. The length of survival after the occurrence of pleural fluid is related to the type of primary tumor, when the tumor is sensitive to drugs, the survival time of those with good systemic and local treatment is longer than those with poor drug efficacy. I. Symptoms of pleural fluid and other clinical manifestations and imaging examinations 1. Common symptoms Difficulty in breathing will occur when there is more pleural fluid, a few people have chest pain, and malignant pleural mesothelioma has more severe chest pain, often local dull pain. Patients with lung cancer often have symptoms such as cough, hemoptysis or blood in sputum. Patients with cancerous pleural fluid often have systemic symptoms such as weight loss, fatigue and loss of appetite. 2.Imaging examinations Except for very few tumors where pleural fluid appears at the time of diagnosis, most of them appear only at the advanced stage of the disease. Ultrasound and chest plain film can determine the amount and changes of pleural fluid, and chest CT can also understand the invasion and metastasis of pleura, intrapulmonary lesions, lymph node metastasis and invasion and metastasis of tumor to surrounding tissues and organs. Other examinations such as PET-CT and MRI should be determined according to the needs of clinical diagnosis and treatment. Thoracentesis, laboratory tests and pathological diagnosis 1. Finding malignant cells in pleural sedimentation or finding cancer in pleural biopsy is the “gold standard” for diagnosing cancerous pleural fluid. In order to clarify the nature of pleural fluid, thoracentesis should be performed for diagnosis. (1) Preparation before puncture: no coagulation disorder and thrombocytopenia, high success rate and safety of ultrasound-guided puncture when pleural fluid is small or encapsulated effusion is formed. (2) Laboratory tests of pleural fluid: the tests include nucleated cell count and classification, total protein, glucose, lactate dehydrogenase and tumor cytology. The chance of detecting cancer cells in one test is about 30%, and the positive rate can be increased to 62%-90% with multiple tests. Certain tumor markers such as CEA, Cyfra21-1, CA125, CA15-3, CA19-9, etc. are helpful for the diagnosis of cancerous pleural fluid. (3) Cancer cells in the pleural fluid sediment of lung cancer patients can also be used to detect EGFR gene mutation and ALK fusion to guide the development of molecular target therapy. In patients with diagnosed lung cancer, when pleural metastasis is present, 95% of them are caused by pleural metastasis. When the pleural fluid is bloody (not caused by puncture injury), it can be diagnosed as cancerous pleural fluid. 2.If cancer cells cannot be detected from pleural fluid and malignancy is highly suspected, closed pleural biopsy and medical thoracoscopy can be used to obtain tumor tissue (biopsy). (1) In 7-12% of patients with negative cytology, the diagnosis can still be confirmed by closed pleural biopsy. However, it should be noted that the positive rate of cancer cells detected by closed pleural biopsy only reaches 40%-75%, which is related to the small extent of tumor involvement in the pleura, failure of pleural biopsy to obtain the tumor site, and inexperience of the operator. (2) Internal thoracoscopy: mainly used for the differential diagnosis of unexplained exudative pleural effusion, also can spray talcum powder to perform pleural fixation via control of pleural fluid. The operator should have some experience, and it is also difficult to take material when the tissue adhesions are serious. Third, treatment The main purpose of treatment is to reduce respiratory distress. Treatment is selected according to the patient’s symptoms and physical condition, the type of primary tumor and response to systemic treatment, and the degree of lung reopening after pleural fluid drainage. The treatment methods include clinical observation, therapeutic thoracentesis, intercostal tube drainage and pleural homotomy, outpatient long-term indwelling chest drainage tube, thoracoscopy and other treatments. 1.Clinical observation Recommended for patients with MPE whose primary tumor is clear but asymptomatic. 2.Thoracocentesis and intercostal tube drainage At present, most of them are punctured under ultrasound localization or ultrasound guidance and placed with fine drainage tube to release chest fluid, which can temporarily relieve respiratory distress. The amount of fluid drained by thoracentesis depends on the patient’s symptoms (cough, chest discomfort). The first puncture should be limited to 600 ml of fluid, with a maximum of 1000 ml, followed by drainage of 1 L every 2 hours, and care should be taken not to release fluid too fast. The drainage should be stopped once the patient develops chest discomfort, persistent cough or vasovagal symptoms during the drainage process. Resuscitated pulmonary edema is a rare and serious complication, often due to long-term compression of the lung, excessive and rapid drainage of the chest water for the first time, or early overuse of negative chest pressure suction to rapidly reopen the atrophied lung. A rapid increase in pleural fluid after puncture suggests the need for additional therapeutic measures as soon as possible. If dyspnea is not relieved after thoracentesis, lymphovascular spread, lung expansion insufficiency, cardiac insufficiency, pulmonary embolism and tumor compression or invasion of blood vessels should be considered. Diagnosis and treatment of cancerous pleural fluid 3. Systemic drug therapy and local drug therapy (1) Some cancerous pleural fluid can be effectively controlled by effective systemic therapy (chemotherapy, targeted therapy and endocrine therapy, etc.). Small cell lung cancer, breast cancer and ovarian cancer are relatively sensitive to chemotherapy, and primary prostate cancer is more sensitive to endocrine therapy. Molecular targeted drugs such as ERSA or crizotinib can often achieve very good results in treating lung adenocarcinoma with EGFR mutation or ALK fusion. For patients who have been treated before, second- or third-line drug therapy is often not effective. (2) Intrathoracic chemotherapy: When the malignant tumor is confined to the thoracic cavity, intrathoracic injection of antitumor drugs can treat the tumor itself in addition to reducing pleural fluid exudation. The commonly used chemotherapeutic drugs are cisplatin. (3) In the past, there were attempts to inject cytokines and other drugs directly into the chest cavity to treat cancerous pleural fluid. The drugs used include interleukin 2 (IL-2), interferon (IFNβ, IFNγ), staphylococcus aureus or mushroom polysaccharide, etc. Some scholars also tried local heat perfusion in the chest cavity. All these methods have varying efficacy, but none of them has been confirmed by multicenter randomized clinical trials with large samples. 4, pleural fixation Patients with intercostal tube drainage alone without pleural fixation have a high recurrence rate of MPE. If there is no significant atrophy of the lung, pleural fixation should be performed after intercostal tube drainage to reduce recurrence. The principle of pleural fixation is that the intrapleural injection of sclerosing agent causes a diffuse inflammatory response in the pleura and activation of the local coagulation system with fibrin deposition, which causes adhesions in the mural and dirty layers of the pleura and eventually leads to the disappearance of the pleural cavity for therapeutic purposes. Intrathoracic injection of sclerosing agent is less commonly used in clinical practice, which can cause pain and require injection of lidocaine into the chest cavity. The commonly used sclerosing agent for pleural fixation is imported medical talcum powder. Bleomycin is another optional sclerosing agent with general efficacy, and each dose is usually 45-60 mg. Other optional sclerosing agents are short rods, doxycycline, tetracycline, etc., with varying efficacy.