Staging systems describe how far a cancer has spread within a human body. Staging helps oncologists determine the most effective course of treatment, as well as the overall prognosis – that is, how well a person will respond to treatments, the potential for cancer recurrence, and expected lifespan. The stage of a cancer is determined by physical exams, X-rays, CT scans, MRIs, PET scans, blood, urine and body fluid laboratory tests, tumor market tests, kidney and liver function tests, and biopsies obtained through micro-surgery or major surgical invasion.
Mesothelioma staging is almost always done with one or both of two methods: (1) overall stage groupings based on Roman numerals, ranging from 0 to IV, with IV the most severe and extensive, and (2) the TNM system. Peritoneal mesothelioma is not typically staged, although oncologists sometimes choose to use the TNM system to characterize this cancer as well.
The acronym TNM stands for Tumor, Nodes, and Metastases, with additional categories of spread or severity described by adding numbers. Thus, for example, a T1N1M0 cancer staging diagnosis provided by an oncologist means that the cancer is of limited involvement (1), involving a lymph node, with no discernible metastases, or spread. A TisN0MX indicates an early, isolated tumor with no lymph node involvement and an inability to evaluate distant metastasis.
The system originated in June 1994 during the Seventh World Conference of the International Association for the Study of Lung Cancer, and – as a staging system for malignant pleural mesothelioma – continues to be the paradigm because it reconciles multiple, former staging systems as well as taking into account new data regarding the influence of the T and N status in overall survival rates.
In Stage I only the outer layer of mesothelial tissues, or pleural lining, is affected. In Stage Ib inner pleural layers have cancerous growth, but only on one side and without spreading into the lungs or diaphragm.
Stages II and III reflect the gradual spread of cancer cells, into the muscle of the chest wall, the diaphragm or the lungs themselves, and potentially into the pericardium, or the mesothelial lining that covers and protects the heart, or the lymph nodes on one side of the chest.
At Stage III, pleural mesothelioma is still surgically treatable – a regimen commonly followed by dual chemotherapy. In Stage IV, however, treatments become palliative, aimed at relieving pain and improving breathing, because the cancer has spread so extensively, and possibly even metastasized to distant locations.
Matching Up the Two Systems
Staging also helps researchers put cancer patients in the appropriate clinical trial, from which they – and medicine at large – may benefit, and gives such researchers a language tool for evaluating clinical trial results. Most important, it allows medical professionals from all venues to communicate quickly and concisely the nature, type and extent of a patient’s cancer.
Staging is based on the way cancer progresses. From a single cell, cancer tissue divides and expands to form a mass, called a growth or tumor. As tumors expand, they can invade nearby organs or other vital tissues, or separate from the growth and spread into the bloodstream or lymphatic system, giving rise to cancers in distant locations of the body. This process is known as metastasis.
The TNM staging system, now one of the most widely used, is favored by such organizations as the International Union Against Cancer (UICC), the American Joint Committee on Cancer (AJCC), and is the industry standard for the National Cancer Institute’s (NCI’s) PDQ reporting system, a comprehensive cancer database.
The NCI’s Surveillance, Epidemiology, and End Results Program, or SEER, continues to use a summary form of staging for all types of cancer, grouping tumors into five main categories:
- Early, or in situ tumors, occurring only in the cells where it originated
- Localized, or present only in the organ where it originated, with no evidence of metastasis
- Regional, or a tumor that has spread to nearby organs, tissues or lymph nodes
- Distant, or cancer which has metastasized to organs or lymph nodes far away from the original site
- Unknown, or cancers of unknown origin, spread, and lethality