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The importance of TNM staging in mesothelioma diagnosis

By Michael Bartlett

Posted on April 29th, 2019

Once the diagnosis of malignant mesothelioma is made by your doctor, further tests such as imaging and biopsy will be performed to check the extent to which cancer has spread in your body. This process - staging - helps doctors start an appropriate treatment plan and improve your prognosis.

Mesothelioma staging is an essential part of the diagnostic procedure and a vital element in creating an individualized treatment plan. It also plays a major role in deciding the patient's eligibility for undergoing tumor removal surgery.

Mesothelioma has four stages: stage 1 mesothelioma is localized, the malignancy has not spread beyond the point of origin, whereas stages 2 through 4 are considered to be advanced stages.

When mesothelioma is diagnosed at a less advanced stage, people tend to have a better chance of getting successful treatment. But, as mesothelioma has a latency period of almost 2-3 decades and symptoms similar to that of other common diseases, many patients remain undiagnosed until they reach the advanced stage 3 or 4. At these stages, patients may have a worse prognosis due to the lack of curative treatment options.

The staging systems were developed specifically to stage malignant pleural mesothelioma. Researchers are working on adapting the TNM system for peritoneal mesothelioma. Because pericardial mesothelioma or testicular mesothelioma are rarer cancers, no formal systems have been created to stage them. The Tumor, Nodes, and Metastasis (TNM) Staging System was first developed in the 1940s by a French physician, Pierre Denoix. In the early 1980s A.P. Chahinian developed the first TNM staging system specific to mesothelioma.

Currently, the TNM staging system is approved by the American Joint Committee on Cancer (AJCC) and is the most commonly used and often updated by new mesothelioma research. It is also referred to as the International Mesothelioma Interest Group (IMIG) staging system. In this system, the factors such as the size of the tumor, its extent, lymph node involvement, and metastasis are taken into account to classify the pleural mesothelioma stage.

Understanding the TNM system

The TNM staging system describes the important aspects of cancer in detail. The letter T stands for the tumor and explains the size and extent of the primary tumor, the letter N describes if the lymph nodes are affected, and the letter M refers to the metastasis or the spread of the tumor from the point of development to other parts of the body.

The tools used in clinical staging and prognostication include physical exams, imaging tests, pathology, and surgical reports, and biopsy results from thoracoscopy along with novel tools, such as MRI imaging-acquisition protocols and CT scan volumetric tumor measurement.

In the TNM system, each letter is followed by a number that provides more details about cancer, and here's what they mean:

Main tumor (T)

  • TX: Tumor cannot be measured
  • T0: Tumor cannot be found
  • T1, T2, T3, and T4: The higher the number following the T, the larger the size of the tumor.

Regional lymph nodes (N)

  • NX: Tumor in the nearby lymph node cannot be measured.
  • N0: No tumor detected in nearby lymph nodes
  • N1, N2, N3: The number of lymph nodes that have been affected. Higher the number, greater is the number of lymph nodes involved.

Distant metastasis (M)

  • MX: Metastasis cannot be measured.
  • M0: There is no spread of cancer to other parts of the body.
  • M1: Cancer has spread to other parts of the body.

TNM staging for mesothelioma

The evaluation of all the above factors places the patient in one of the following 4 stages. In January 2018, the TNM system was updated to include subcategories such as stage 1A and stage 1B.

Stage 1A: localized

  • Denoted as T1 N0 M0, this is the earliest stage of mesothelioma, in which cancer has developed in the pleura (membrane lining) on one side of the chest wall, the lining near the diaphragm, the area between the lungs (mediastinum) or the pleura covering the lung.

Stage 1B: localized

  • T2 N0 M0: Mesothelioma developed in both layers of the pleura and has grown into the breathing muscle or lung tissue.
  • T3 N0 M0: Mesothelioma has developed in both layers of the pleura and has spread to one of the following:
    • Fatty tissue between the lungs
    • The first layer of the chest wall
    • Place within the deeper layer of the chest wall
    • The outer layer of the lining of the heart

Stage 2: the first advanced stage

  • T1-T2 N1 M0: Mesothelioma has developed in the pleura lining on one side of the chest wall (T1) and may have grown into the breathing muscle or the lung itself (T2). It has also spread to lymph nodes on the same side of the chest as the main tumor (N1).

Stage 3A: advanced

  • T3 N1 M0: In this subcategory, cancer has spread from the pleura into a layer of the chest wall, the outer layer of the heart lining or the fatty tissue between the lungs. Cancer has also spread to lymph nodes on the same side of the chest as the main tumor (N1).

Stage 3B: advanced

  • T1 T3 N2 M0: The main tumor may or may not have spread beyond the pleura (T1-T3), but cancer cells have spread to lymph nodes on the other side of the chest or above the collarbone (N2).
  • T4, Any N, M0: Mesothelioma has developed in both layers of the pleura and may or may not have spread into lymph nodes. It has also spread into any one of the following places:
    • More than one place in deeper layers of the chest wall (the muscle or ribs)
    • The breathing muscle and into the abdominal lining (peritoneum)
    • Any organ between the lungs (esophagus, trachea, thymus and blood vessels)
    • Spine
    • The other side of the chest
    • Through the heart lining or into the heart

Stage 4: advanced

Any T, Any N, M1: By this stage, mesothelioma may or may not have spread into places near the main mass (any T). It may or may not have spread to lymph nodes (any N) but has spread to distant places such as the bones, liver, lungs, abdominal lining or lining of the lungs on the other side of the chest (M1).

Importance of the TNM system in the diagnostic process

First and foremost, the physicians who follow the TNM staging system can group your diagnosis into categories, which helps in determining the appropriate stage. Accurate staging is important as it determines your eligibility for certain treatment procedures. In addition, it helps:

  • To understand the severity of cancer and chances of survival
  • To select the best treatment plan
  • To identify clinical trials that patients may enroll in

At Environmental Litigation Group, P.C., we collaborate with a medical research team that follows the TNM staging of cancer to ensure you get the most accurate diagnosis. Also, it's important to keep in mind that regardless of the stage of mesothelioma you have been diagnosed with, you are entitled to receive financial compensation and you can file compensation claims with bankruptcy trusts or with the VA, if the asbestos exposure occurred in the military.

If you, or a family member, have been diagnosed with mesothelioma, it's important for you to contact an experienced mesothelioma lawyer. We offer a free initial consultation and you don't have to pay anything upfront when you hire our asbestos law firm.