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How Staging Systems Describe a Mesothelioma Diagnosis
Doctors use staging systems to track and measure the progression of cancer. Combined with diagnostic procedures such as biopsies and radiological imaging, cancer staging allows physicians to finalize a prognosis and cancer treatment plan.
Imaging tests such as CT-scan, MRI or PET measure the size and distribution of tumors as well as identify lymph node involvement or metastatic disease. A February 2022 research study noted that advanced CT image textures have the potential to differentiate between mesothelioma tumor cell types.
Staging systems translate these diagnostic results into a number system that oncologists use to give cancer a “stage.”
There are four stages of pleural mesothelioma: stages 1 and 2 are early in the disease process, and stages 3 and 4 involve widespread tissue involvement or multiple tumors.
These stages differ slightly depending on the staging system. Historically, there have been three staging systems used for pleural mesothelioma, but TNM is the commonly accepted method.
- TNM: Tumor Node Metastasis is the most-used staging system for malignant pleural mesothelioma and also provides the most information. A number after each letter details the presence and extent of tumor mass throughout the body.
- Butchart: The oldest mesothelioma staging system, the Butchart method, is based on the location of the primary tumor and has mostly fallen out of use. This system does not account for tumor size or overall tumor mass in the body.
- Brigham: Dr. David Sugarbaker, a pioneer of mesothelioma treatment, developed this system at Brigham and Women’s Hospital. The Brigham method emphasizes the feasibility of surgery through each stage of progression.
There are no formal staging systems for pericardial mesothelioma or testicular mesothelioma.
TNM Staging System
This is the most widely used system for pleural mesothelioma. It is also called the iMiG Staging System after the International Mesothelioma Interest Group, which is the organization that developed it.
The abbreviation TNM signifies three different parts of a mesothelioma diagnosis. Doctors add a number after each letter to describe how far cancer has advanced. A modified version of this system loosely defines the stages of peritoneal mesothelioma as well.
The TNM staging system is a three-part description that defines cancer by tumor classification, lymph node classification and metastasis classification.
Pleural Mesothelioma Tumor Classifications
The T in TNM staging describes the size and location of primary tumor tissue. T values range from T0 to T4, with higher values indicating larger tumors or deeper tissue involvement.
- Tx: The primary tumor is not measurable or is undetermined.
- T0: The primary tumor is not present.
- T1: Tumors are present on one side of the chest involving the parietal pleura and may extend into the visceral pleura on the same side.
- T2: Tumors remain on one side of the chest and have developed into the diaphragm muscle, inner lung tissue or both.
- T3: Tumors extend into the deeper fat tissues of the chest wall, the mediastinum between the lungs or the pericardium around the heart.
- T4: The pleura on one or both sides of the chest contains multiple, nonresectable tumors in addition to tumors involving the ribs, spine or heart.
Pleural Mesothelioma Lymph Node Classifications
The N values in the TNM staging system describe cancer lymph node involvement. When cancer reaches a lymph node near its origin, it can spread to secondary sites and form new tumors.
- Nx: Lymph nodes near the primary tumor site are undeterminable.
- N0: Regional lymph nodes have no evidence of cancer.
- N1: There is evidence of metastasis on lymph nodes near the primary cancer site on the same side of the body.
- N2: Lymph nodes on the opposite side of the primary tumor, or above the clavicle level, show signs of metastasis.
Pleural Mesothelioma Metastasis Classifications
Metastasis occurs when tumors have spread from their original location to distant areas in the body, forming new sites of cancer growth. The M value indicates whether metastasis is present or absent.
- M0: There are no signs of metastasis, and cancer is stage 3 or below.
- M1: Metastasis has occurred outside the region of the primary tumor. An M1 notation automatically classifies cancer as stage 4.
Together, the T, N and M values determine the stage of mesothelioma from 1 to 4. Stages 1 and 3 also have substages 1A, 1B, 3A and 3B.
Stage 1A: T1 N0 M0
The earliest stage of mesothelioma, stage 1A, indicates tumor involvement on one side of the chest, possibly in deeper tissues of the pleura around the diaphragm or the mediastinum between the lungs. In this stage, cancer has not reached the lymph nodes or metastasized.
Stage 1B: T2 N0 M0 or T3 N0 M0
In stage 1B, a T2 tumor has invaded the diaphragm muscle or inner lung tissue. A T3 tumor may still be surgically removable, but it has advanced into deeper fat tissues in the chest wall, mediastinum or pericardium, the protective sac surrounding the heart.
Stage 2: T1-2 N1 M0
In stage 2, cancerous cells have spread from the tumor to nearby lymph nodes on the same side. Tumors haven’t extended into deeper fat or muscle tissue, but cancerous lymph nodes indicate a risk of metastasis.
Stage 3A: T3 N1 M0
The first type of stage 3 mesothelioma means cancer has reached the chest wall, heart lining or the mediastinum, and a lymph node on the same side.
Stage 3B: T1-3 N2 M0 or T4, Any N, M0
Cancerous cells in stage 3B have spread to lymph nodes opposite the origin site. If the tumor is T4, it is unresectable and has extended into one or multiple areas near the chest, spine or heart.
Stage 4: Any T, Any N, M1
Pleural mesothelioma is stage 4 if distant metastasis has occurred, regardless of T or N value. Metastasis sites typically include the liver, kidneys, bone, abdominal lining, inner lung or pleural lining on the other lung.
TNM for Peritoneal Mesothelioma
In 2011, the Peritoneal Surface Oncology Group International proposed a staging system for peritoneal mesothelioma. To create the staging system, the group gathered data on peritoneal patients who had surgery with heated chemotherapy.
This system has not been formally adopted, but many doctors use it to define three peritoneal mesothelioma stages.
A fourth stage has not been created yet because this system is based on patients who qualified for surgery. Researchers did not have enough data to define a fourth stage because only early-stage patients qualify for surgery.
In the future, a fourth stage will likely be defined. Until then, doctors generally define the fourth stage as when the cancer spreads to distant parts of the body.
T1 N0 M0: Presence of tumors is minimal and contained within the abdominal lining (peritoneum).
T2-T3 N0 M0: Tumors are moderate and contained in the abdominal lining.
T4 N0-N1 M0-M1: Presence of tumors is extensive (T4) and may or may not have spread to lymph nodes (N0-N1) or beyond the abdominal lining (M0-M1).
T1-T4 N1 M0-M1: Tumors may range from minimal to extensive (T1-T4). The cancer has spread to lymph nodes (N1) and may or may not have spread outside the abdominal lining (M0-M1).
T1-T4 N0-N1 M1: Presence of tumors may range from minimal to extensive (T1-T4). The cancer may or may not have spread to lymph nodes (N0-N1), but has spread outside the abdominal lining (M1).
Early Staging Systems
Before the adoption of the TNM system, oncologists used two other methods for staging pleural mesothelioma. In 1998, Dr. David Sugarbaker developed the Brigham staging system, which focused on surgery and whether a patient is eligible at different stages of progression.
Dr. Eric Butchart devised the first mesothelioma staging system in 1976, but the technique is not commonly used and is limited in detail.
Brigham Staging System
The Brigham staging system was created by Dr. David Sugarbaker at the Brigham and Women’s Hospital in Boston. With this system, doctors look at organs, tissues and other parts of the body to learn how far pleural mesothelioma has spread.
This system is primarily designed to determine whether a patient qualifies for surgery. In the first two stages, tumors are small and easier to remove. In stage 3 and stage 4, the cancer has grown and spread and it is not easy to operate.
Tumors are only in the lining of the lungs, and cancer has not spread to the lymph nodes. Surgery is an option.
Tumors are within the lining of the lungs. Lymph nodes near the tumors are cancerous. Surgery is an option.
Inoperable tumors are in the lining of the lungs and have spread into one or more of the following:
- The area between the lungs
- The chest wall
- The breathing muscle
- Distant lymph nodes
Cancer has spread to distant parts of the body. Surgery is not an option.
Butchart Staging System
Dr. Eric Butchart created this system in 1976 to make sure patients got the right treatment.
Now retired, Butchart was a cardiothoracic surgeon at the University Hospital of Wales in the United Kingdom when he developed this staging system.
Butchart realized aggressive treatment worked better for patients with small tumors that had not spread far. He based his staging system on this fact, which helped doctors decide what treatments would work best for each patient.
This system is outdated and no longer used, but it helped other doctors develop the staging systems we use today.
The cancer affects the pleura on only one side of the chest and may have spread to the heart lining and diaphragm.
Cancer has spread to the chest wall and may affect both sides of the pleura. It may have spread to the esophagus, heart or lymph nodes of the chest.
Cancer has spread to the breathing muscle or abdominal lining (peritoneum). Mesothelioma cells have also traveled through the lymphatic system to lymph nodes outside the chest.
The cancer has spread through the bloodstream to distant parts of the body. Tumors may now be present in the bones, liver, brain or other organs.
Staging System Updates
As researchers gather more knowledge on the progression of malignant pleural mesothelioma, the criteria that define each stage may change again. An evolving staging system equips doctors with the knowledge to offer treatment plans tailored to distinct stages.
The most recent change was the eighth edition of the TNM system for malignant pleural mesothelioma published by the American Joint Committee on Cancer in 2018.
Prominent changes included collapsing T1a and T1b into just T1, refining N components by eliminating the N3 category, and changing stage 4 to be concerned only with the presence of metastasis.
Over time, mesothelioma staging systems will continue to offer more defined diagnoses, allowing physicians to treat patients with more significant effect and higher chances of survival.