Invasive procedures
There are various invasive procedures that may be performed to help diagnose and stage malignant mesothelioma. These procedures are more complicated than non-invasive tests, usually require some form of anesthesia, and may involve a stay in hospital.

Thoracentesis. This is the drainage of fluid from a pleural effusion, using a fine needle (passed through the skin of the chest wall, between the ribs), which is often guided using ultrasonography. The fluid is then looked at under a microscope, to determine the type and characteristics of the cells present (cytology). However, in malignant mesothelioma, cytology often gives negative or indeterminate results. Thoracentesis may relieve symptoms of breathlessness caused by a pleural effusion.
Thoracoscopy or pleuroscopy involve the use of an endoscope to look inside the chest or within the pleural space and see how widespread the suspected tumor is. The examining doctor may see nodules on the parietal pleura (in early disease) or in more advanced disease, diffuse areas of tumor or even a thick 'cake' of tumor spreading over the surface of the lung. These procedures also allow the doctor to take multiple biopsies from throughout the pleura/tumor, to confirm if the tumor is malignant mesothelioma or some other cancer, and what type of malignant mesothelioma it is. Thoracoscopy is said to be nearly 95% as accurate as open thoracotomy.
Open lung biopsy. This is a major procedure that involves opening the chest wall (thoracotomy) to access the lungs. Multiple biopsies are then taken from the tumor and any involved lungs. It is recommended that normal lung specimens are also taken, so any asbestos fibers can be counted (for litigation purposes).
Bronchoscopy is the use of a rigid endoscope, which is passed into the airways of the lungs. It is used to define the anatomy within the lung, and to make sure there is no cancer within the lung airways (bronchogenic carcinoma) in patients being considered for aggressive surgical therapy. (Surgery is not suitable for those with disease within the airways).
Laparoscopy. This is use of an endoscope to visualize the abdominal cavity, to assess whether tumor has spread through the diaphragm and across the peritoneum. It is sometimes performed before patients undergo aggressive surgery, because spread of tumor into the abdominal cavity rules out surgery.
Many of these procedures carry a risk of 'seeding' tumor along the needle tract. For this reason, radiation therapy is often given before they are performed, to prevent this from happening.