Mesothelioma Diagnosis and Staging

January 24, 2025

This page was reviewed under our medical and editorial policy by Jyoti Malhotra, M.D., M.P.H., associate professor, Department of Medical Oncology & Therapeutics Research, City of Hope^® Orange County Lennar Foundation Cancer Center; and Jae Y. Kim, M.D., associate professor, Division of Thoracic Surgery, Department of Surgery, City of Hope Cancer Center Duarte

Mesothelioma is a rare cancer that begins in cells lining internal organs, known as the mesothelium. Most cases are caused by asbestos exposure. Mesothelioma may not be diagnosed until a person begins having symptoms, such as shortness of breath and chest pain, as there are no screening tests for the general population. 

Doctors may recommend that those who have been exposed to asbestos undergo regular imaging tests, such as chest X-rays or computed tomography (CT) scans. These imaging tests may show changes in the lungs over time, but they may not detect mesothelioma in its early stages.

Mesothelioma Testing

Tests for mesothelioma differ according to its location in the body. Areas that may be affected include:

• The pleura, a thin layer of tissue that covers the lungs and lines the inside of the chest cavity
• The peritoneum, which lines the abdominal cavity and covers many of the organs within it
• The pericardium, which covers the heart and the space around it
• The tunica vaginalis, which lines the testicles

Blood tests may be performed to check for the presence of Fibulin-3 and soluble mesothelin-related peptides (SMRPs). These markers may be elevated in people who have mesothelioma.

In a lab, a pathologist uses a microscope to examine samples of a patient’s tissue or bodily fluid to see if cancer cells are present. Because mesothelioma may look like other types of cancer under a microscope, further testing is typically needed to confirm a diagnosis.

Members of the care team work with patients and their families to determine what tests for mesothelioma should be completed.

Pleural Mesothelioma Testing

Tests for pleural mesothelioma, which affects the lungs and chest wall, may include the following.

Chest X-ray: This may detect changes in the pleura, such as thickening or calcium deposits, or changes to the lungs themselves. Chest X-rays may also show fluid in the area between the chest wall and the lungs.

Computed tomography (CT) scan: A CT scan may be performed on any part of the body to help find the cancer. A CT scan may also help with staging, which measures the extent of the cancer and guides treatments. Comparing CT scans over time may reveal whether treatments are working to shrink the cancer or slow its growth.

Positron emission tomography (PET) scan: For a PET scan, radioactive sugar is injected into the patient’s bloodstream where it is taken up by cancer cells. Then, a special camera is used to show the areas of radioactivity. Doctors may use this test after a CT scan to determine if changes to the lungs or peritoneum owe to scar tissue or to cancer.

Magnetic resonance imaging (MRI): MRI with or without gadolinium contrast may help detect mesothelioma of the diaphragm, the thin muscle that separates the heart and lungs from the abdomen.

Thoracentesis: For this test, a health care provider uses a needle to withdraw fluid from the chest area. The sample is then checked for the presence of cancer cells.

Needle biopsy: Doctors use imaging, such as a CT scan, to guide placement of a needle into the space between the lungs. They take samples of tissue from this area and check to see if cancer has spread. Because the amount of tissue taken is very small, the results of this test may not be conclusive.

Thoracoscopy: For this test, doctors use a thin tube with a tiny camera on the end (thoracoscope) to look inside the chest and obtain samples of tissue from the pleura. The patient is under general anesthesia for the procedure.

Mediastinoscopy: This test helps doctors examine the space behind the breastbone. A small incision is made on the chest and a small tube with a camera on the end is inserted to check the area (mediastinum). This test is done under general anesthesia in an operating room. Mediastinoscopy may help distinguish between lung cancers and mesothelioma, and may reveal whether cancer has begun to spread.

Endobronchial ultrasound needle biopsy: A thin tube with an ultrasound device on the end is inserted into a patient’s windpipe (trachea) to see if cancer has spread to the lungs and lymph nodes nearby. A needle may be inserted through the tube to obtain biopsy tissue for examination under a microscope. Endobronchial ultrasound biopsy may be performed with numbing drugs or under general anesthesia.

Thoracotomy: A surgeon makes an opening in the chest wall and takes larger tissue samples for a lung biopsy. In some cases, the entire tumor may be removed.

Pulmonary function tests: For this test, a person breathes in and out of a tube that is connected to a machine. It measures how well the lungs are working and helps doctors decide if the patient is healthy enough to undergo surgery. Doctors also use it to get an idea of how much lung tissue to remove.

Pericardial Mesothelioma Testing

Tests for pericardial mesothelioma, which affects the heart and surrounding tissue, may include the following.

Echocardiogram: If doctors suspect there is fluid around a person’s heart (pericardial effusion), they may order an echocardiogram, a computer picture created by high-energy sound waves. This ultrasound test also helps show how well the heart is working.

Pericardiocentesis: A health care provider uses a needle to remove fluid from the sac (pericardium) around a person’s heart. The sample of fluid is checked to see if cancer cells are present.

Peritoneal Mesothelioma Testing

Tests for peritoneal mesothelioma, which affects the abdominal region, may include the following.

Paracentesis: For this test, the health care provider uses a needle to remove fluid from the patient’s abdomen. The sample is checked to see if cancer cells are present.

Laparoscopy: Doctors insert a thin tube with a tiny camera on the end (laparoscope) into the abdominal cavity to check for tumors. This procedure is performed with the patient under general anesthesia in an operating room.

Laparotomy: The surgeon makes an opening in the abdominal wall and takes larger biopsy samples. Sometimes, the entire tumor may be removed.

Tunica Vaginalis Mesothelioma Testing

Tunica vaginalis mesothelioma is a cancer affecting the lining of a man’s testicles. Doctors may deploy several tools during the diagnostic process, such as the following.

Ultrasound: Also called ultrasonography, this painless test uses high-frequency sound waves and a wand guided across the affected area to create pictures of tissue in and around the testicles.

Positron emission tomography (PET) scan: For this test, radioactive sugar is injected into a person’s blood where it is taken up by cancer cells. Then, a special camera is used to show the areas of radioactivity in the body. Doctors may use this test after an ultrasound of the testicles to see if areas of abnormality are cancerous.

Pelvic MRI: This imaging test may show if tumors are present in the testicles.

Mesothelioma Stages

Mesothelioma is diagnosed based on the results of a physical exam, imaging and biopsy tests. Doctors then use this information to assign a stage to the cancer. Staging categories describe how much cancer is in the body and how far it has spread. Staging also helps doctors determine which mesothelioma treatments to use and helps them discuss survival statistics.

Though there are several types of mesothelioma, malignant pleural mesothelioma (MPM) is the only type that is formally staged because the other types are less common. The staging system that is typically used is the American Joint Committee on Cancer (AJCC) TNM system, in which:

• T refers to the size of the tumor
• N indicates if cancer has spread to lymph nodes
• M refers to metastases, which means the cancer has spread to distant sites in the body

Each letter may be followed by a number, which indicates how advanced the cancer is. A lower number means the cancer is less advanced, while a higher number means it is more advanced.

The current MPM system is described below. Experts are also looking at ways to enhance the staging system by using both clinical staging (based on imaging tests, exam and biopsy) and pathological staging (based on surgery to remove a tumor), as well as the measurement of the size of the tumor.

Stage 1

Stage 1 MPM may be broken down as follows.

Stage 1a (T1, N0, M0): The cancer is on one side of the chest wall in the pleural lining. It may also be in the diaphragm, the space between the lungs (mediastinum) or the pleura that covers the lung. No lymph nodes are involved, and the cancer has not spread to other parts of the body.

Stage 1b (T2, N0, M0): The cancer is on one side of the chest wall in the pleural lining and is also in the pleura that covers the diaphragm, the mediastinum and the lung. Cancer has grown into the diaphragm or the lung, but no lymph nodes are involved, and the cancer has not spread to other parts of the body.

Stage 1b (T3, N0, M0): The cancer has grown into nearby tissues but may still be removed with surgery. It is on one side of the chest wall in the pleural lining and may also be in the pleura that covers the diaphragm, the mediastinum and the lung. While cancer has not spread to lymph nodes or other areas, it has grown into at least one of the following:

• The first layer of the chest wall (endothoracic fascia)
• Fatty tissue of the mediastinum
• One single area deep in the chest wall
• The top layer of the tissue covering the heart (pericardium)

Stage 2

Stage 2 MPM is in the pleural lining on one side of the chest. It may also have grown into the diaphragm or the lung. At this stage, the cancer has spread to nearby lymph nodes on the same side of the body as the tumor, but not beyond.

Stage 3

Stage 3 MPM may be classified as the following.

Stage 3a (T3, N1, M0): While cancer has grown into nearby tissues, surgical removal may still be possible. The cancer is on one side of the chest lining and also in the pleura that covers the diaphragm, the mediastinum and the lung. The cancer has spread to nearby lymph nodes on the same side of the body as the tumor. It has not spread to other areas. But, it has grown into at least one of the following:

• The first layer of the chest wall (endothoracic fascia)
• Fatty tissue of the mediastinum
• One single area deep in the chest wall
• The top layer of the tissue covering the heart (pericardium)

Stage 3b (T1-T3, N2, M0): The cancer may or may not have grown into nearby tissues, and surgery to remove it may still be possible. Cancer has spread to nearby lymph nodes on the other side of the body and may also have reached lymph nodes above the collarbone (supraclavicular lymph nodes) on either side of the body. It has not spread elsewhere.

Stage 3b (T4, any N, M0): The cancer has grown too much to be removed completely with surgery. It is on one side of the chest wall in the pleural lining and also in the pleura that covers the diaphragm, the mediastinum and the lung. Cancer may also have spread to nearby lymph nodes, but it has not spread to other areas of the body. It has grown into at least one of the following:

• More than one area deep in the chest wall, including the muscle or ribs
• Through the diaphragm into the abdominal lining (peritoneum)
• Any organ in the mediastinum, such as the esophagus, trachea, thymus or surrounding blood vessels
• The spine
• The pleural lining on the other side of the chest
• Through the pericardium or into the heart

Stage 4

Stage 4 MPM may or may not have spread to nearby tissues or lymph nodes. At this stage, the cancer has spread to distant organs, such as the bones, liver, peritoneum or opposite lung.