What Is the TNM Staging System?
There are many different types of cancer staging systems that help classify cancers based on specific characteristics. The Butchart staging system, Brigham staging system and TNM staging system are all used in mesothelioma staging, as well as the Peritoneal Cancer Index (PCI) in the case of peritoneal mesothelioma. The TNM staging system is the most common, as it is frequently updated based on the most recent mesothelioma research.
The TNM staging system was created by Dr. Pierre Denoix in the 1940s at the Institut Gustave-Roussy in France. The system is maintained by the American Joint Committee on Cancer (AJCC) and the Union for International Cancer Control (UICC). In addition to pleural mesothelioma, the TNM system can be used to classify other cancers like lung cancer.
The “T” component of TNM includes the location and extent of the primary tumor. “N” refers to lymph node involvement, particularly whether or not the cancer has spread to the lymph nodes or if they are left unaffected. “M” refers to metastasis, and if the cancer is confined to nearby areas or if distant spreading has occurred. Together, these three components can guide pleural mesothelioma staging.
Understanding the TNM Classification
When classifying tumor extent, tumors are given a designation of T1, T2, T3, or T4, depending on the size of the primary tumor site or nearby tissues that are affected. Tumor extent alone cannot classify the cancer, but rather must be considered in combination with lymph node involvement and metastasis.
- T1: Tumor involves only the ipsilateral parietal or the visceral pleura
- T2: Tumor involves the parietal or visceral ipsilateral pleural and has also invaded the diaphragmatic muscle and/or the pulmonary parenchyma
- T3: Tumor involves the parietal or visceral ipsilateral pleura and has also invaded one or more additional areas, including the endothoracic fascia, mediastinal fat, chest wall or pericardium
- T4: Tumor involves the parietal or visceral ipsilateral pleura and has also invaded one or more additional areas, including the endothoracic fascia, mediastinal fat, chest wall, peritoneum, contralateral pleural, mediastinal organs, vertebrae, neuroforamen, spinal cord, brachial plexus or pericardium
Lymph node involvement is graded as NX, N0, N1 or N2. In early stages, cancer has either not spread to the lymph nodes at all or has only spread to nearby lymph nodes. In the later stages, distant lymph nodes are affected.
Lymph Node Involvement
- NX: Regional lymph nodes can’t be assessed
- N0: No regional lymph node metastasis
- N1: Metastasis involving the ipsilateral intrathoracic lymph nodes
- N2: Metastasis involving the contralateral intrathoracic lymph nodes, and metastasis to the ipsilateral or contralateral supraclavicular lymph nodes
Metastasis plays an important role in TNM classification. Grading is simple with either a grade of M0 or M1. M0 indicates no metastasis while M1 indicates that the cancer is no longer localized and has spread to distant areas of the body. In the case of malignant pleural mesothelioma, this likely indicates that the cancer has spread to the opposite side of the chest involving the abdominal lining. With M0, the cancer is either stage 1, stage 2 or stage 3. M1 places the patient at stage 4 regardless of T or N stage.
- M0: No distant metastasis
- M1: Distant metastasis has occurred
Determining TNM Stages
Experts use a variety of methods to pinpoint mesothelioma stage using the TNM technique, including physical exams, imaging tests, pathology reports, surgical reports and biopsy results. Physicians can then determine where the cancer is located, figure out type, see if the tumor has grown, test for cancerous cells in other parts of the body and provide other information crucial to making an accurate diagnosis and providing patients with a prognosis.
After determining tumor extent, lymph node involvement and potential metastasis, physicians use the TNM guidelines to classify the cancer as stage 1A, stage 1B, stage 2, stage 3A, stage 3B or stage 4.
|3B||T1, T2, T3 or only T4||Only N2 or N0, N1, N2||Mo|
|4||Any T||Any N||M1|
Stage will not only help determine patient prognosis, but will give physicians a better idea of what mesothelioma treatment options are best.
Resources for Mesothelioma Patients
TNM Staging System Updates
The latest version of the TNM system is the 8th Edition of the TNM Classification for Malignant Pleural Mesothelioma, which is reflected in the latest AJCC Cancer Staging Manual. Updates to the system were made by the IASLC Staging and Prognostic Factors Committee (SPFC) and approved by the UICC and AJCC. This particular version was implemented in January 2017 but not widely implemented in the United States until January 2018.
Experts continue to update aspects of the staging system as new information emerges through research and clinical trials regarding mesothelioma, treatment and staging techniques.