Various staging systems have been used for mesothelioma during the past 3 decades since its recognition. The first staging system for mesothelioma was published by American Joint Commission on Cancer (AJCC) and was accepted International Union Against Cancer. This publication appeared in the fifth edition of AJCC Cancer Staging Manual. The current staging system used by AJCC is the staging system proposed by International Mesothelioma Interest Group (IMIG) in the year 1995. This staging system is based on the relationship between tumor size, nodal status, and overall survival. This staging system applies to only those tumors that arise from the pleura. Peritoneal and pericardial mesotheliomas are rare and are difficult to classify in terms of tumor size and nodal and metastatic status.
Primary site (T)
The mesothelium from which the mesothelioma originates covers the external surface of the lungs and inside of the chest wall. Mesothelium consists of flat, tightly connected cells, which are one layer thick.
Regional lymph nodes (N)
The lymph nodes located in the internal mammary chain, intra-thoracic area, scalene lymph nodes, and supraclavicular lymph nodes may be involved with mesothelioma. These designations are identical to the designations used for lung cancer.
Distant metastasis (M)
Distant metastasis of pleural mesotheliomas may occur to retroperitoneal lymph nodes, brain, and spine. Most common site of metastatic spread is peritoneum, pleural surface on the other side and lung.
IMIG staging system for malignant pleural mesothelioma
Primary tumor (T)
TX: Primary tumor cannot be assessed
T0: No evidence of primary tumor
T1: Tumor involves same side pleura of the chest wall, with or without focal involvement of the pleura on the outer side of lung
T1a: Tumor involves same side pleura of the chest wall, no involvement of pleura on the outer surface of lung
T1b: Tumor involves same side pleura of the chest wall with focal involvement of pleura on the outer surface of lung
T2: Tumor involves same side pleura of the chest wall with at least one of the following features:
Confluent tumor on the outer surface of the lung
Involvement of the muscles of the diaphragm
Involvement of the lung tissue deeper to the mesothum covering the lung
T3: Tumor involves same side pleura of the chest wall with at least one of the following features:
Involvement of the endothoracic fascia
Involvement of the mediastinal fat
Single focus of tumor involving the soft tissue of the chest wall
Involvement of pericardium just on the out aspect (without penetration of pericardium
T4: Tumor involves same side pleura of the chest wall with at least one of the following features:
Diffuse or multi-focal involvement of the soft tissue of the chest wall
Involvement of the rib
Invasion through the diaphragm to the peritoneal cavity
Invasion of any mediastinal organ
Direct extension to the pleura on the other side
Invasion into spine
Penetration of the pericardium
Pericardial effusion which is positive for cancer cells
Involvement of heart muscle
Involvement of the nerves of brachial plexus
Lymph node involvement (N)
NX: Regional lymph nodes cannot be assessed
N0: No regional lymph node involvement
N1: Involvement of same side bronho-pulmonary and or hilar lymph nodes only
N2: Involvement of subcarinal lymph node(s), and or same side or opposite side internal mammary or mediastinal lymph node(s)
N3: Involvement of opposite side mediastinal, internal mammary, or hilar lymph node(s) and or same side or opposite side supraclavicular or scalene lymph node(s)
Distant metastasis (M)
Mx: Distant metastasis cannot be assessed
M1: No distant metastasis
M1: Distant metastasis present
Staging
Stage 1
T1 N0M0
Stage IA
T1a N0M0
Stage IB
T1b N0 M0
Stage II
T2, N0 M0
Stage III
T1, T2 N1 M0
T1, T2, N2, M0
T3, N0, N1, N2, M0
Stage IV
T4 Any N M0
Any T N3 M0
Any T Any N, M1
Probably the most important prognostic factor in patients with mesothelioma may be the tumor burden. Prognosis in patients with small tumor and no involvement of lymph nodes are significantly superior compared to those with those patients who have bigger tumor size and involvement of the lymph nodes. Higher stage by itself is a poor prognostic factor in malignant mesothelioma. Further prognostic factors for mesothelioma will be discussed elsewhere in this article.
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