01. Defining the TNM Staging System
What Is the TNM Staging System?
The TNM classification system uses three components to determine cancer stage:
- Tumor extent (T): The location and size of the primary tumor site
- Lymph node involvement (N): Whether the cancer has spread to nearby lymph nodes
- Metastasis (M): Whether the cancer is localized or has spread to distant areas of the body
A doctor scores each component and assigns a value. A doctor will use the scores to determine the mesothelioma stage between 1 and 4.
The system is maintained by the American Joint Committee on Cancer (AJCC) and the Union for International Cancer Control (UICC).
Other Mesothelioma Staging Systems
In 1994, the International Mesothelioma Interest Group (IMIG) published the first widely accepted TNM classification for malignant pleural mesothelioma. Although the TNM system is most commonly used, there are other systems used to stage mesothelioma.
Less common staging systems for mesothelioma are:
- The Butchart staging system
- The Brigham staging system
In some cases, doctors have used a modified TNM system to stage peritoneal mesothelioma. The Peritoneal Cancer Index (PCI) is also used for staging peritoneal mesothelioma.
02. Understanding TNM Classification
How Doctors Use the TNM System to Classify Cancer
To determine mesothelioma stage using the TNM system, doctors will score each category of the system using letters and numbers. Tumor extent, lymph node involvement and metastasis together determine the overall stage.
In some cases, doctors may update staging information after surgical removal of tumors. This is called surgical staging.
Surgery allows physicians to visualize and assess tumor size and spread. Therefore the surgical stage may differ slightly from the clinical stage.
Classifying Tumor Extent
Tumors are given a designation of T1, T2, T3 or T4. The designation depends on the size of the primary tumor site and its spread to nearby tissues.
Pleural Mesothelioma Tumor Classifications
- Tx: The primary tumor is unknown/undetermined
- T0: No evidence of primary tumor
- T1: Tumors located on a single side (only the left or the right) of the parietal pleura, with or without tumors on the visceral pleura of the same side
- T2: Tumor(s) on every surface of the pleura on one side of the body with at least one of the following: tumors covering the entire surface of the visceral pleura; tumors on the diaphragm muscle; and/or tumors within the lung tissue
- T3: Tumor(s) on every surface of the pleura on one side of the body with at least one of the following: tumor(s) on the lining between the parietal pleura and the ribs (endothoracic fascia); tumor(s) extending into the fatty tissue in the space between the lungs (the mediastinum); completely resectable tumors within the soft tissues of the chest wall; and/or tumor(s) on a portion of the pericardium, not extending through the full thickness of the pericardium
- T4: Tumor(s) on every surface of the pleura on one side of the body with at least one of the following: multiple, non-resectable tumors within the soft tissues of the chest wall; tumor(s) of/in the ribs; tumor(s) of/in the heart, trachea or esophagus; tumors on both sides of the pleura (left and right); tumors in the spine or the nerves in the shoulder (brachial plexus); tumors extending through all layers of the pericardium; and/or tumors in the heart muscle
Although tumor size and extent may provide an indication of prognosis, it alone cannot classify the cancer stage. It must be considered in combination with lymph node involvement and metastasis.
Classifying Lymph Node Involvement
Lymph node involvement is the spread of cancerous cells from the primary tumor site to nearby lymph nodes.
In early stages, cancer has either not spread to the lymph nodes at all or has only spread to nearby lymph nodes. In later stages, distant lymph nodes are affected.
Lymph node involvement is graded as NX, N0, N1 or N2.
Lymph Node Classification for Mesothelioma
- NX: Regional lymph nodes can’t be assessed
- N0: No regional lymph node metastasis
- N1: Metastases in the regional lymph nodes on the same side as the primary tumor(s), excluding lymph nodes above the clavicle
- N2: Metastases in the regional lymph nodes on the opposite side from the primary tumor or to the lymph nodes above the clavicle on either side of the body
Lymph node involvement is an important factor for staging mesothelioma. If cancer cells spread to the lymph nodes, it increases the likelihood of distant metastasis in the body. As cancer spreads, patients may face more limited treatment options and a less favorable prognosis.
Cancer metastasis is the spread of cancer from its origin. Metastasis can lead to tumors growing beyond the primary tumor site in distant areas of the body.
Mesothelioma metastasis plays an important role in TNM classification. It is scored as either M0 or M1.
Metastasis Classification for Mesothelioma
- M0: Indicates no metastasis. The cancer is either stage 1, stage 2 or stage 3.
- M1: Indicates the cancer is no longer localized and has spread to distant areas of the body. The cancer is at stage 4 regardless of T or N classification.
In pleural mesothelioma cases, metastasis may indicate cancer has spread to the opposite side of the chest and abdominal lining.
Resources for Mesothelioma Patients
03. Determining Mesothelioma Stage
Determining Mesothelioma Stage Using the TNM System
After each category of the TNM system is scored, the doctor combines the information in a process called stage grouping. During stage grouping, physicians classify the mesothelioma cancer as:
- Stage 1A or 1B
- Stage 2
- Stage 3A or 3B
- Stage 4
In the earlier stages, mesothelioma is considered less advanced and patients may be eligible for more aggressive treatment options, such as invasive surgery. Later stages may signify mesothelioma cells have spread to distant parts of the body, which may limit a patient’s treatment options.
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Determining stage allows mesothelioma doctors to provide patients with an accurate prognosis. Typically, patients diagnosed with mesothelioma in stage 1 and stage 2 have better survival rates than those diagnosed in stage 3 or stage 4 cancer.
Other Factors That Impact Prognosis
Factors that may impact mesothelioma survival rate include:
Physicians will assess prognosis based on the TNM stage and unique patient characteristics. These factors also help clinicians determine the best way to move forward with treatment.
04. TNM System Updates
TNM Staging System Updates
The latest version of the TNM system is the eighth edition of the TNM classification for malignant pleural mesothelioma. The most up-to-date version is reflected in the latest AJCC Cancer Staging Manual.
Updates to the system were made by the International Association for the Study of Lung Cancer (IASLC) Staging and Prognostic Factors Committee (SPFC). The UICC and AJCC approved the updates.
The eighth edition was implemented in January 2017 but was not widely used in the United States until 2018.
Mesothelioma research is consistently improving diagnostic tools and treatments. Updates to the TNM system help doctors provide patients with the most accurate prognosis and treatment plan.