The TNM Classification of Malignant Tumours (TNM) system was designed by Professor Pierre Denoix in the 1940’s to assist in the staging of cancerous tumors. The staging system focuses on evaluating the primary tumor, what the tumor has invaded locally, and if the cancer has spread beyond the local area.
This system of diagnosis assists doctors in describing the metastatic progress of a cancer in ways that are meaningful to assisting in prognosis and treatment. It is used by the American Joint Committee on Cancer (AJCC). The staging consists of 3 elements: T, N, M.
T: T describes the primary tumor size and whether local tissues have been invaded. Diagnoses include T0, T1, T2, T3, and T4.
T0: No signs of tumor
T1: Small tumor, not invaded beyond the site of origin. For pleural mesothelioma this would mean a cancer located in the pleura lining of the chest wall on one side, with possible growth into the pleura lining of the diaphragm, the space between the lungs (mediastinum), or the pleura covering the lung.
T2: Larger local growth than T1. For pleural mesothelioma this would involve a tumor growth that had invaded not just the pleura lining of the chest wall, but also the pleura coating of the diaphragm and/or the pleura covering the lung. It may have also invaded the local organs itself, the lung or diaphragm.
T3: More locally invasive than T2. For pleural mesothelioma this would indicate the criteria of T2 plus at least one of:
- tumor presence in the endothoracic fascia chest wall
- tumor presence in the fatty tissue of the mediastinum
- tumor presence in the deep layers of the chest wall, or
- tumor presence in the pericardium layer covering the heart.
T4: Pervasive local invasion. T4 cancer is likely to be impossible to remove locally with surgery due to the presence of tumor growth throughout the local tissue and organs surrounding the primary tumor. For pleural mesothelioma a T4 diagnosis would indicate tumor presence in the pleura lining, pleura coating of the lung, diaphragm, mediastinum, and at least one of the following:
- multiple locations of the deep chest wall
- through the diaphragm into the peritoneum
- other organs
- the spine
- across the chest to the opposite side of chest, or
- into the heart.
N: N describes the regional lymph node involvement. N diagnosis include N0, N1, N2 or N3.
N0: No tumor presence in the local lymphatic system.
N1: Tumor located in local lymphatic system. For pleural mesothelioma this indicates a presence of cancer in the hilar or bronchial lymph nodes on the same side as the primary tumor.
N2: An in-between diagnosis for tumors that exhibit some aspects of N1 and N3 involvement. For pleural mesothelioma, a diagnosis of N2 indicates presence of tumor to the subcarinal or mediastinal lymph nodes. It may also include growth into the internal mammary lymph nodes under the breastbone, or the peridiaphragmatic nodes of the diaphragm.
N3: The tumor is located in lymphatic nodes beyond the local tumor, or multiple locations within local lymph nodes. For pleural mesothelioma a N3 diagnosis means tumor growth beyond one side of the chest or a tumor that has spread to the supraclavicular lymph nodes in the collarbone.
M: M describes metastatis distant from the primary tumor. M is diagnosed as M0 or M1.
M0: No distant metastasis.
M1: Metastasis has occurred in distant organs. The cancer has spread to other organs.
The TNM staging system can be used to diagnose mesothelioma into Stage 1, Stage 2, Stage 3, or Stage 4 mesothelioma. Each of these stages corresponds to a different treatment and prognosis, and is based upon the diagnosis of stages of T, N, and M:
Stage 1 Mesothelioma: T1, N0, M0: A stage 1 mesothelioma diagnosis is rare for a mesothelioma, as a patient would typically remain asymptomatic. For pleural mesothelioma this would mean local growth into the plueral cells only without any invasion into lymph nodes or organs. This is the most treatable diagnosis of mesothelioma.
Stage 2 Mesothelioma: T2, N0, M0: For pleural meosthelioma, a stage 2 diagnosis indicates the tumor has grown beyond the pleura lining and into the coating of the diaphragm, lung, or space between the lungs, as well as the diaphragm or lung organs. It is still treatable with surgery, given the lack of lymph node involvement or movement to distant sites.
Stage 3: Multiple possibilities exist for TNM staging and Stage 3 mesothelioma:
T1/T2, N1/N2, M0: Stage 1 or Stage 2 development of the primary tumor (T1/T2), plus involvement into the lymph nodes (N1/N2). It has not spread to distant sites or distant organs.
T3, N0/N1/N2, M0: Stage 3 development but the primary tumor has also advanced into the fatty tissue of the mediastinum or into the heart itself. This could involve lymph node progression (N1 or N2) or not, but regardless of lymphatic involvement the primary tumor has advanced significantly into the local tissue and organs (T3).
Stage 4: The highest stage of mesothelioma diagnosis:
By stage IV pleural mesothelioma has greatly advanced. It indicates the diagnosis of T4 or massive local involvement of the local tissue, a N3 diagnosis of significant involvement of the lymphatic system, and may or may not also include a M1 diagnosis of distant metastatic movement into distant tissues and organs.
To read about each stage and prognosis, follow these links for more information:
Stage 1 Mesothelioma & Prognosis
Stage 2 Mesothelioma & Prognosis
Stage 3 Mesothelioma & Prognosis
Stage 4 Mesothelioma & Prognosis