A tissue sample from the tumour (a biopsy) will usually be needed to confirm the diagnosis.

Needle biopsy
You may be given a needle biopsy. First you will be given a local anaesthetic to numb the area, and a special type of needle is then passed through your skin into the tumour. A sample of tissue is then cut out. This is often done at the same time as fluid drainage. Your doctor or radiologist may do this using a CT scanner to guide the process.

These procedures are not associated with a high risk of complications. However, your doctor will explain that there is a small risk of internal bleeding after the biopsy, and a small risk of air leaking from your lung with a pleural biopsy. Even if they occur, these problems often settle without needing treatment. However, it may be necessary to have a chest X-ray after the biopsy to check for these complications.

If the results later confirm a mesothelioma tumour, there is a chance that tumour cells may have settled in the scar where your biopsy was taken. This might eventually cause a small swelling. It may be possible to prevent this by having a small dose of radiotherapy to the drain site once the mesothelioma diagnosis is confirmed.

Needle biopsy is sometimes called fine needle aspiration cytology (FNAC).

Surgical biopsy
If the initial tests have not given a definite answer, but the doctor suspects there is still a chance that you may have a tumour, a surgical biopsy may be needed. You will be admitted into hospital. The operation is done while you are under a general anaesthetic. Keyhole surgery is usually used. Three small cuts are made between the ribs and into the pleura (the membrane lining the lungs). This lets the surgeon insert a camera, a light source and an operating instrument. The surgeon can then take biopsies and remove any fluid. Often, sterile talc is used as a glue to stick the layers of the pleura together and prevent fluid from coming back