How is mesothelioma diagnosed?

Blood tests and x-rays can provide information about your overall health and help to rule out other conditions.

Blood test

You will have blood taken to check your general health and let your doctors know how your blood cells, liver and kidneys are working. This helps them work out whether you’re fit enough for treatment. Mesothelioma does not usually show up with a blood test, but results may show substances called markers that are produced by cancer cells.

X-ray

If your doctor thinks you have pleural mesothelioma, you will have a chest x-ray to look for any changes in the lungs, thickening of the pleura, and fluid in the space between the lungs and the chest wall.

For peritoneal mesothelioma, an x-ray will look for changes in the abdomen, such as fluid and thickening in the peritoneum.

If fluid, thickening or other changes are found, you will need more tests to check whether mesothelioma or another condition is the cause.  Sometimes mesothelioma will not show up on an x-ray but can be seen on a CT scan.

A CT (computerised tomography) scan uses x-rays and a computer to create a detailed picture of the inside of the body. Most people can go home as soon as the test is over.

Before the scan, you will be given a dye called contrast to make the pictures clearer. This is usually injected into a vein in your arm, but is sometimes given as a drink. The dye may make you feel hot all over and leave a strange taste in your mouth for a few minutes. You might also feel that you need to urinate, but this won’t last long.

During the scan, you will need to lie still on a table that moves in and out of the CT scanner, which is large and round like a doughnut. The scan takes about 30 minutes. Although the test itself is painless, lying flat and still can be uncomfortable if you already have breathlessness or pain. Let your doctor know before the scan if you have claustrophobia, as the scanner is a confined space.

The CT scan shows the location and thickness of the tumour(s) in the chest or abdomen. It can also show if the mesothelioma has spread to other organs. The information from the CT scan is used to work out the best way to get tissue for testing.

A biopsy is the main test used to diagnose mesothelioma. It involves removing a sample of tissue, which is examined under a microscope by a specialist doctor called a pathologist. The pathologist looks for cell changes to work out if the tumour is mesothelioma and, if so, the type of mesothelioma cells present.

Mesothelioma is usually classified according to how the cells look under a microscope (although in about 27% of cases, the classification is unknown). There are three main types of mesothelioma cells:

Epithelioid – cells look similar to normal mesothelial cells. This is the most common type, making up about 70% of cases.

Sarcomatoid – cells have changed and look like cells from fibrous tissue. This type makes up about 10–15% of cases.

Mixed or biphasic – has epithelioid and sarcomatoid cells. This type makes up about 10–15% of all cases.

Ways to take a biopsy for mesothelioma

A biopsy can be taken in different ways. The choice of biopsy will depend on your general health and fitness, and how suitable the tumour is for sampling using one of the methods below. Keyhole surgery (VATS or laparoscopy) is the most common biopsy technique as both tissue samples and fluid can be removed for testing. However, obtaining a sample can be challenging, so a respiratory physician or gastroenterologist, radiologist, surgeon and pathologist may all be involved.

Video-assisted thoracoscopic surgery (VATS) – This is used to obtain a tissue sample from the lining of the lungs (pleura). You will be given a general anaesthetic, then a thin tube with a light and camera will be inserted through a few small cuts in your chest. Tissue samples can be taken through the tube and sent to a laboratory for testing. After the VATS you’ll need painkillers.

Laparoscopy – This is used to get a tissue sample from the lining of the abdomen (peritoneum). You will be given a general anaesthetic, then a thin tube with a light and camera will be inserted through small cuts made in your abdomen. Tissue samples can be removed through the tube and sent to a laboratory for testing. If fluid has built up in the abdomen, it can be drained during the laparoscopy. Any infections that develop will be treated with antibiotics.

CT-guided core biopsy – A CT-guided core biopsy may be used instead of VATS or laparoscopy when there is a large mass but no fluid. You will have a local anaesthetic to numb the area, and a hollow needle will be inserted through the skin to remove a thin core of tissue from the lining of the lungs or abdomen. A CT scan will be used to guide the needle into position.

During a CT-guided core biopsy, you will need to lie still on a table for about 30 minutes. Afterwards you will stay in the radiology suite for a couple of hours so you can be watched for possible complications (such as bleeding or a collapsed lung).

Draining fluid

When you first have symptoms of mesothelioma, you are likely to have a build-up of fluid in the space around your lungs or in your abdomen. Fluid around the lungs (pleural effusion) can make it hard to breathe. Fluid in the abdomen (ascites) may make it swollen and uncomfortable.

Before suggesting further tests or treatment, your doctor may drain the built up fluid to ease symptoms. When fluid is drained from the pleura, it is called a pleural tap, pleurocentesis or thoracentesis; when it is drained from the peritoneum, it is called a peritoneal tap or paracentesis.

Draining the fluid may be done at the same time as VATS or laparoscopy.

PET scan – The specialised PET or positron emission tomography scan is being used more often. It is available at some major hospitals and may not be covered by Medicare for mesothelioma. For the PET scan, a small amount of radioactive glucose solution will be injected into a vein, usually in your arm. You will need to sit quietly for 30–90 minutes while the solution travels through your body. Your whole body will then be scanned for raised levels of radioactive glucose. Cancer cells show up brighter on the scan pictures because they are more active and take up more of the glucose solution than normal cells do.

Special stains – To confirm a diagnosis of mesothelioma, the pathologist sometimes needs to do further tests on the tissue sample using special stains. These look for specific molecules that may help to tell mesothelioma apart from other types of cancer.

Diagnosis from fluid samples

Sometimes a fluid sample rather than a tissue sample may be used to make a diagnosis because it’s easy to collect fluid when draining the pleural or peritoneal cavity. However, it can be hard to diagnose mesothelioma from fluid samples because abnormal mesothelioma cells can look similar to other cells.

Using fluid samples for diagnosing mesothelioma may be useful if you are not well enough for a biopsy.