The Stages of Malignant Mesothelioma
IMIG System (Proposed in 1995)
In 1995, the International Mesothelioma Interest Group (IMIG) proposed a new staging systems for identifying mesothelioma. The IMIG System, which was a revitalized version of the TNM system, was a basic framework used to create what is now known as the International TNM system.
The IMIG system was introduced in order to identify more precise TNM descriptors that can be used for more accurate radiographic, surgical, and pathologic staging of malignant pleural mesothelioma (MPM). The IMIG staging system takes into consideration histologic type and suggests that patients should be stratified according to whether they have epithelial tumors or one of the other histologic subtypes of MPM to more clearly identify mesothelioma stage.
It was not adopted by the medical community because it raised more questions about the prevelance and role of N1, N2, and N3 nodal metastases and the influence that these nodal groups may have on patient outcomes.
However, this staging system led to future clinical trials and some within the medical community believe the TNM staging should be used with the IMIG system to stratify patients by histologic type to more clearly assess treatment strategies and survival rates.
Below is the revised international staging system proposed by the International Mesothelioma Interest Group for staging diffuse malignant pleural mesothelioma in 1995:
T = Tumor
T1
T1a Tumor limited to the ipsilateral parietal including mediastinal and diaphragmatic pleura
No involvement of the visceral pleura
T1b Tumor involving the ipsilateral parietal including mediastinal and diaphragmatic pleura
Scattered foci of tumor also involving the visceral pleura
T2 Tumor involving each of the ipsilateral pleural surfaces (parietal, mediastinal, diaphragmatic, and visceral pleura) with at least one of the following features:
{bullet} Involvement of diaphragmatic muscle`
{bullet} Confluent visceral pleural tumor (including the fissures), or extension of tumor from visceral pleura into the underlying pulmonary parenchyma
T3 Describes locally advanced but potentially resectable tumor
Tumor involving all of the ipsilateral pleural surfaces (parietal, mediastinal, diaphragmatic, and visceral pleura) with at least one of the following features:
{bullet}Involvement of the endothoracic fascia
{bullet}Extension into the mediastinal fat
{bullet}Solitary, completely resectable focus of tumor extending into the soft tissues of the chest wall
{bullet}Nontransmural involvement of the pericardium
T4 Describes locally advanced technically unresectable tumor
Tumor involving all of the ipsilateral pleural surfaces (parietal, mediastinal, diaphragmatic, and visceral) with at least one of the following features:
{bullet}Diffuse extension or multifocal masses of tumor in the chest wall, with or without associated rib destruction
{bullet}Direct transdiaphragmatic extension of tumor to the peritoneum
{bullet}Direct extension of tumor to the contralateral pleura
{bullet}Direct extension of tumor to one or more mediastinal organs
{bullet}Direct extension of tumor into the spine
{bullet}Tumor extending through to the internal surface of the pericardium with or without a pericardial effusion; or tumor involving the myocardium
N = Lymph nodes
NX Regional lymph nodes cannot be assessed
N0 No regional lymph node metastases
N1 Metastases in the ipsilateral bronchopulmonary or hilar lymph nodes
N2 Metastases in the subcarinal or the ipsilateral mediastinal lymph nodes including the ipsilateral internal thoracic nodes
N3 Metastases in the contralateral mediastinal, contralateral internal thoracic, ipsilateral, or contralateral supraclavicular lymph nodes
M = Metastases
MX Presence of distant metastases cannot be assessed
M0 No distant metastasis
M1 Distant metastasis present
Stage I
Ia T1a N0 M0
Ib T1b N0 M0
Stage II T2 N0 M0
Stage III Any T3 M0
Any N1 M0
Any N2 M0
Stage IV Any T4
Any N3
Any M1
