Staging of Mesothelioma

Once someone is diagnosed with pleural mesothelioma, the next step is determining the stage of the cancer. Evaluating staging means gauging danger by answering some fundamental questions. Have tumors metastasized (spread) through the lining of the lung? If so, how far did they progress? If not, how contained are they?

Answers to these questions lead to treatment options and to a potential prognosis. The earlier that the cancer is caught, the more likely the patient will receive a prognosis of increased life span. Different treatment options are also more viable during these early stages.

To determine the stage of someone's mesothelioma, doctors can schedule a variety of diagnostic tests. These may include biopsies, blood tests or imaging scans like X-rays, CT scans or PET scans. Results from these tests reveal crucial information about the cancer that helps doctors select the best treatments and determine the patient's survival outlook. They can also assist doctors with finding relevant clinical trials that may benefit the patient.

For most cancers, including pleural mesothelioma, doctors assign a stage in the form of a Roman numeral. The Roman numerals range from I to IV, with more advanced cancers having a higher stage number. To translate the results of diagnostic tests into an accurate stage, doctors use what is called the TNM staging system.

Developed in the early 1940s, the TNM system has been specialized for many types of cancer over the years. It continues to evolve as scientists learn more about how cancer grows and spreads throughout the body.

In 1995, the International Mesothelioma Interest Group (IMIG) developed a formal staging system for pleural mesothelioma based off of the TNM system. This uniform system is used internationally to give doctors a common way to describe the disease, which is crucial for guiding clinical trials and treatment of the disease.

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TNM Staging System

The TNM Staging System centers on three factors that describe key aspects of the patient's cancer:

GroupDescription
TStands for tumor and describes the size of the primary tumor and the extent of its spread.
NStands for nodeandevaluates the extent of cancer spread to nearby lymph nodes, which are small, oval-shaped organs of the immune system where cancer typically spreads first.
MStands for metastasis and indicates whether the cancer has metastasized, or spread, to distant organs or lymph nodes.

Once a doctor evaluates the patient's cancer for TNM characteristics, a number or letter is added to each letter to further describe the progression of cancer. The numbers begin at zero and increase as the cancer advances. If any factor can't be assessed for some reason, an X is used.

For pleural mesothelioma, the meaning behind the letters and numbers attached to each factor is as follows:

Tumor (T Group)

For the T group, numbers following the T increase based on the size of the primary tumor and how much it has grown into nearby tissues.

StageFactor
TXThe main tumor cannot be assessed.
T0There is no evidence of a primary tumor.
T1aThe mesothelioma tumor involves the lining of the chest wall (parietal pleura) on one side of the chest, but not the lining of the lung surface (visceral pleura). It may also affect the pleural lining of the breathing muscle (diaphragm) or the space between the lungs (mediastinum).
T1bThe tumor involves both the parietal and visceral pleura on one side of the chest. It may also affect the diaphragm or mediastinum.
T2The tumor involves the pleural lining of the chest wall on one side of the chest, as well as the pleural lining of the diaphragm, mediastinum and the lung. The cancer has also grown into at least one of the following:
  • The diaphragm muscle
  • Tissue of the lung itself
T3The mesothelioma is considered locally advanced, but may still be able to be removed surgically. The tumor involves the pleura lining the chest wall and the pleura lining the lung, diaphragm and mediastinum on one side of the chest. It has also grown into at least one of the following:
  • The outermost layer of the chest wall (endothoracic fascia)
  • Fat tissue of the mediastinum
  • A single focus of tumor in the soft tissues of the chest wall
  • The outer surface of the lining of the heart (pericardium)
T4The mesothelioma is considered technically unresectable, meaning it cannot be completely removed surgically. The tumor involves the pleura lining the chest wall and the pleura lining the lung, diaphragm and mediastinum on one side of the chest. It has also grown into at least one of the following:
  • Multiple locations within the inner layers of the chest wall, including the muscle, ribs or soft tissues
  • The lining of the abdominal cavity (peritoneum) via the diaphragm
  • Any organ in the mediastinum, such as the esophagus, trachea, thymus or blood vessels
  • The spine
  • The pleura on the opposite side of the chest
  • Muscle of the heart

Node (N Group)

For the N group, numbers following the N describe the location, size and number of lymph nodes affected by the cancer. The more cancerous lymph nodes there are, the higher the N number.

StageFactor
NXNearby lymph nodes cannot be assessed.
N0There is no spread to nearby lymph nodes.
N1Cancer has spread to lymph nodes in the lung and/or the hilar lymph nodes, located near the area where the bronchus enters the lung. Only lymph nodes on the same side of the chest as the main tumor are affected.
N2Cancer has spread to other lymph nodes on the same side of the chest as the main tumor, such as subcarinal lymph nodes and mediastinal lymph nodes. N2 also includes spread to lymph nodes behind the breastbone and near the diaphragm.
N3Cancer has spread to supraclavicular lymph nodes near the collarbone on either side and/or hilar lymph nodes on the side of the chest opposite the main tumor.


Metastasis (M Group)

For the M group, only two numbers are used to describe the extent of the cancer's spread throughout the body.

GroupDescription
M0There is no spread to distant parts of the body.
M1Cancer has spread to distant organs or lymph nodes.

Roman Numeral Staging

Once cancer doctors assign values to the T, N and M categories with data from diagnostic tests or surgical techniques, they combine the values into a string of letters and numbers that give an accurate depiction of the extent of cancer at diagnosis.

T1aN0M0, for example, indicates there is a mesothelioma tumor on the pleural lining of the chest wall with no lymph node involvement and no sign of spread to distant organs. With this information, doctors can then assign a Roman numeral stage that plays an important role in pleural mesothelioma treatment and research.

Using the previous example of T1aN0M0, doctors would refer to this diagnosis as a Stage IA tumor. While the mesothelioma may progress further, the stage at diagnosis stays the same throughout treatment.

The table below lists each Roman numeral stage for pleural mesothelioma and the corresponding TNM values.

StageTNM
IT1N0M0
IAT1aN0M0
IBT1bN0M0
IIT2N0M0
IIIT1,T2
T1,T2
T3
N1
N2
N0,N1,N2
M0
M0
M0
IVT4
Any T
Any T
Any N
N3
Any N
M0
M0
M1
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