How is malignant mesothelioma staged?

Staging is the process of finding out how far a cancer has spread. Your treatment and prognosis (outlook) depend, to a large extent, on the cancer’s stage. 

Staging is based on the results of physical exams, biopsies, and imaging tests (CT scan, PET scan, etc.), which are described in the section, “How is malignant mesothelioma diagnosed?”

A staging system is a formal way for doctors and nurses to sum up the extent of a cancer. Pleural mesothelioma, the most common type, is the only mesothelioma for which a formal staging system exists.

The TNM staging system

The system most often used to describe the growth and spread of pleural mesothelioma is the American Joint Committee on Cancer (AJCC) TNM staging system. The TNM system is based on 3 key pieces of information:

• T sums up the extent of spread of the main (primary) tumor.
• N describes how much the cancer has spread to nearby (regional) lymph nodes. Lymph nodes are small bean-shaped collections of immune system cells to which cancers often spread first.
• M indicates whether the cancer has spread (metastasized) to other organs of the body. (The most common sites are the pleura on the other side of the body, the lungs, and the peritoneum.

Numbers or letters appear after T, N, and M to provide more details about each of these factors. Higher numbers mean the cancer is more advanced.

T groups

TX: The main tumor can't be assessed for some reason.

T0: There is no evidence of a main tumor (the cancer is found elsewhere instead).

T1: Mesothelioma involves the pleura lining the chest wall on one side of the chest. It may or may not also affect the pleura lining the diaphragm (the breathing muscle) or the mediastinum (the space between the lungs). It may also have spread to the pleura covering the lung.

T2: Mesothelioma involves the pleura lining the chest wall on one side of the chest. It also involves the pleura coating the diaphragm, the mediastinum, and the lung. It also has grown into at least one of the following:

• The diaphragm
• The lung itself

T3: The mesothelioma has grown further but may still possibly be removed with surgery. The tumor involves the pleura lining the chest wall on one side of the chest. It also involves the pleura coating the lung, the diaphragm, and the mediastinum. It also has grown into at least one of the following:

• The first layer of the chest wall (called the endothoracic fascia)
• The fatty tissue in the mediastinum
• A single place in the deeper layers of the chest wall
• The surface of the pericardium (outer covering layer of the heart)

T4: The mesothelioma has grown too far to be removed completely with surgery. The tumor has grown into the pleura lining the chest wall on one side of the chest. It also is in the pleura coating the lung, diaphragm, and mediastinum on the same side. It also has grown into at least one of the following:

• More than one place in the deeper layers of the chest wall, including the muscle or ribs
• Through the diaphragm and into the peritoneum
• Any organ in the mediastinum (esophagus, trachea, thymus, blood vessels)
• The spine
• Across to the pleura on the other side of the chest
• Through the heart lining (pericardium) or into the heart itself

N groups

NX: The nearby lymph nodes can't be assessed.

N0: No spread to nearby lymph nodes.

N1: Spread to lymph nodes within the lung and/or around the area where the bronchus enters the lung (called hilar or bronchial lymph nodes) on the same side as the main tumor.

N2: Spread to other lymph nodes on the same side as the main tumor, such as the subcarinal (around the point where the windpipe branches into the left and right bronchi) and the mediastinal lymph nodes. Also includes spread to the lymph nodes in the space just behind the breastbone (called internal mammary lymph nodes) and those near the diaphragm (called peridiaphragmatic).

N3: Spread to lymph nodes near the collarbone on either side (supraclavicular lymph nodes), and/or spread to hilar or mediastinal lymph nodes on the side opposite the main tumor.

M groups

M0: No spread to distant organs or areas.

M1: The cancer has spread to distant sites. This can be to distant lymph nodes or to other organs.

Stage grouping for pleural mesothelioma

Once the T, N, and M categories have been assigned, this information is combined in a process called stage grouping to assign an overall stage of I, II, III, or IV. The stages identify tumors that have a similar prognosis and thus are treated in a similar way. Patients with lower stage numbers tend to have a better prognosis.

Stage I

T1, N0, M0: Mesothelioma has grown into the pleura lining the chest wall on one side of the chest. It might or might not also affect the pleura lining the diaphragm (the breathing muscle) or the mediastinum (the space between the lungs). It may also have spread to the pleura covering the lung (T1). It has not spread to the lymph nodes (N0) or to distant sites (M0).

Stage II

T2, N0, M0: Mesothelioma has grown into the pleura lining the chest wall on one side of the chest. It also is in the pleura coating the diaphragm, the mediastinum, and the lung. The cancer has also grown into the diaphragm or the lung itself (T2). It has not spread to the lymph nodes (N0) or to distant sites (M0).

Stage III

Either of the following:

T1 or T2, N1 or N2, M0: Mesothelioma has grown into the pleura lining the chest on one side, and might or might not have grown into the pleura lining the lung, the diaphragm, or the mediastinum. It might also have grown into the muscle of the diaphragm or the lung itself (T1 or T2). It has spread to lymph nodes in the chest on the same side as the main tumor (N1 or N2). It has not spread to distant sites (M0).

OR

T3, N0 to N2, M0: Mesothelioma is in the pleura lining the chest on one side, and has grown into the first layer of the chest wall, the fatty tissue in the mediastinum, a single place in the deeper layers of the chest wall, or the outer covering layer of the heart. It might or might not have spread to lymph nodes in the chest on the same side as the tumor but has not spread to lymph nodes near the collarbone or on the opposite side of the chest (N0, N1, or N2). It has not spread to distant sites (M0).

Stage IV

Any of the following:

T4, any N, M0: Mesothelioma has grown into the pleura lining the chest on one side and has grown into more than one place in the deeper layers of the chest wall (including the muscle or ribs), through the diaphragm and into the peritoneum, into any organ in the mediastinum, into the spine, across to the pleura on the other side of the chest, and/or through the heart lining or into the heart itself. It might or might not have spread to lymph nodes (any N). It has not spread to distant sites (M0).

OR

Any T, N3, M0: The tumor may or may not have grown into nearby tissues (any T). It has spread to lymph nodes near the collarbone on either side and/or to hilar or mediastinal lymph nodes on the side opposite the main tumor (N3). It has not spread to distant sites (M0).

OR

Any T, any N, M1: The mesothelioma might or might not have grown into nearby tissues (any T). It might or might not have spread to the lymph nodes (any N). It has spread to distant sites (M0).

Resectable versus unresectable cancer

The TNM system divides mesotheliomas into several stages that help give doctors an idea about a person’s prognosis (outlook). But for treatment purposes, doctors often use a simpler system based on whether these cancers are likely to be resectable (where all visible tumor can be removed by surgery) or unresectable. 

In general terms, most stage I, II, and III mesotheliomas are potentially resectable, but there are exceptions. Whether or not the cancer can be removed depends not only on how far the tumor has grown into nearby tissues, but also on its subtype (most doctors believe only epithelioid and mixed/biphasic tumors are potentially resectable), where it is located, and if the patient is healthy enough to have surgery. 

Even for resectable mesotheliomas, in most cases cancer cells that cannot be seen are left behind after surgery. For this reason, many doctors use other forms of treatment (radiation therapy and/or chemotherapy) along with surgery when possible.

Other prognostic factors

Stage is an important factor in predicting a patient’s prognosis (outlook), but other factors also play a role. Some factors linked to longer survival times include:

• Good performance status (being able to carry out normal tasks of daily life)
• Younger age
• Epithelioid subtype
• Not having chest pain
• No significant weight loss
• Normal levels of a substance in the blood called LDH
• Normal red blood cell counts, white blood cell counts, and blood platelet counts