TNM Mesothelioma Staging System

The TNM system breaks down as follows:

T = Primary tumor
N = Regional lymph nodes
M = Distant metastasis (the spread of cancer through the bloodstream to other organs)

A number is used with each letter to indicate the size of the tumor and the degree to which it has spread. For "T" and "N", "0" is used to indicate no invasion of tissues or spread; "4" means extensive involvement. For "M", "0" means no metastasis and "1" means there are metastases. For example, a cancer that is classified as T2N0M0 is one that has a measurable, mid-sized tumor but has not spread to lymph nodes and shows no metastases.

When applied to pleural mesothelioma, TNM information is used to categorize the disease into four stages:

• Stage I: The mesothelioma involves the lining on either the left or right side of the chest. The cancer can be found only on the outer lining of the lung, is present in only a few small spots and has not yet reached the lymph nodes.
• Stage II: The mesothelioma involves the lining on either the left or right side of the chest and has spread into the outer lining of the lung, the diaphragm (the muscle separating the chest from the abdomen), or into the lung itself.
• Stage III: The mesothelioma involves the lining on either the left or right side of the chest and has spread into the first layer of the chest wall, the fatty part of the mediastinum (the space in the chest cavity behind the breastbone and in between the two pleural sacs that contain the lungs), a single place in the chest wall, the pericardium, or lymph nodes anywhere in the same side of the chest.
• Stage IV: The mesothelioma involves the lining on either the left or right side of the chest and has spread into the chest wall; through the diaphragm; into the esophagus, trachea, thymus, or blood vessels contained in the mediastinum; into the spine; across to the lining on the other side of the chest; through the pericardium or into the heart itself; into the nerves leading to the arm; into lymph nodes outside that side of the chest; or to other organs via the bloodstream.

For peritoneal mesothelioma, the TNM stages are:

• Stage I: The mesothelioma is localized, with the tumor able to be completely removed surgically.
• Stage II: The mesothelioma is contained within the abdominal cavity on peritoneal and organ surfaces and surgical removal of much of the tumor, but not all of it, is possible.
• Stage III: The mesothelioma is contained within the abdominal cavity but has spread to organs such as the colon or liver.
• Stage IV: The mesothelioma is no longer contained within the abdominal cavity but has spread to other areas of the body.

The TNM system, broken down more specifically, looks like this:

T Stages

T1: Mesothelioma has affected pleura on one side and has reached to the pleura surrounding the lung.
T2: Mesothelioma involves the pleura on either side and also affects the chest lining. The cancer has spread to the outer lining of the lung; into the lung; or into the diaphragm. 
T3: Mesothelioma involves the pleura on either side and affects the chest's outside layer; any place in the chest wall; the fatty area of the area of the chest that holds organs (mediastinum); or the heart's outermost layer.
T4: Mesothelioma involves the pleura on either side and has spread into the chest wall, affecting either the muscle or ribs; through the diaphragm; into any organ in the mediastinum; into the spinal column; to the opposite side of the chest; through the lining of the heart or into the heart itself; or into the brachial plexus.

N Stages

N0: The cancer has not reached the lymph nodes.
N1: Mesothelioma has reached the lymph nodes on the same side of the chest as the first tumor.
N2: Mesothelioma has spread to the lymph nodes; to where the windpipe splits to; or to lymph nodes in behind the bones of the chest and front of the heart. The affected lymph nodes are on the same side as the impacted lung.
N3: The cancer has spread into the lymph nodes in the collarbone area, on either side, to the hilar or mediastinal lymph nodes on the side opposite the cancerous lung.

M Stages

M0: The cancer has not spread to other organs or body parts
M1: The cancer has spread to other parts of the body
This type of staging is completed by combining the T, N and M categories and assigning a stage of I, II, III, or IV.

Stage I (T1, N0, M0): Mesothelioma involving either side of the pleura has spread to the lung's outer layer. It has not reached the lymph nodes or other body parts.

Stage II (T2, N0, M0): Mesothelioma involves either side of the pleura and has reached the outermost lung lining; into the lung; or into the diaphragm. It has not reached the lymph nodes or other body parts.

Stage III (T1 or 2, N1 or 2, M0; OR T3, N0-2, M0): Mesothelioma involves the pleura on either side of the chest and may or may not have reached the outermost lung lining; into the lung; the diaphragm. It has reached the chest's lymph nodes on the same side as the first tumor. The cancer has not spread to other body parts.

OR mesothelioma involves the pleura on either side of the chest and has reached the first layer of the chest; or the fatty area of the mediastinum; or any part of the chest wall; or the heart's outer layer. The cancer may or may not have spread to the lymph nodes. However, it has not spread to the lymph nodes near the collarbone or on the side of the chest opposite the primary tumor. It has not reached other body parts.

Stage IV (T4, any N, M0; OR any T, N3, M0; OR any T, any N, M1): Mesothelioma involves the pleura on either side of the chest and has grown into the chest wall, either the muscle or ribs; through the diaphragm; into any organ in the mediastinum; into the spine; to the opposite side of the chest; through heart's lining or into the heart; or into the brachial plexus. The cancer may or may not have spread to the lymph nodes. It has not reached other body parts.

OR the tumor may be any size and has reached lymph nodes near the collarbone, to hilar or mediastinal lymph nodes, but has reached to lymph nodes near the collarbone on either side, to hilar or mediastinal lymph nodes on the side of the chest opposite the impacted lung, but has not reached other body parts.

OR it has spread to other body parts.