The various stages of cancer are defined in the American Joint Committee on Cancer’s (AJCC) Cancer Staging Manual.
Here is the general description of the TNM staging system. The specific definition for each category is, however, dependent on the type of cancer that is staged using this system.
- Tumor (T): “T” along with a number from 0 to 4 describes the size (measured in centimetres) and location of the tumor. It is a representation of how much the tumour has grown into nearby tissues.
- Node (N): “N” along with a number from 0 to 3 refers to the extent of the spreading of cancer in the lymph nodes. Thus, the more the lymph nodes with cancer, the larger the number assigned. Also, in some tumours, the location of the lymph nodes with cancer might be used to define the “N” category.
- Metastasis (M): “M” indicates whether the cancer has invaded other tissues in other parts of the body. If the cancer is contained withing a specific tissue, it is labeled M0, and if spread, it is labeled M1.
Cancer stage definitions
A combination of the T, N, M results and other factors specific to cancer can be used to determine the stage of cancer:
- Stage 0: Cancer in situ, which means “in place” (not metastasized yet)
- Stage I: Early-stage cancer which is usually small and yet not spread to the lymph nodes or other body parts.
- Stage II and Stage III: Larger cancers or tumours that have grown more deeply into nearby tissue and might have also spread to lymph nodes, but not to other parts of the body yet.
- Stage IV: Advanced or metastatic cancer that has spread to lymph nodes and other parts of the body.
Depending on the specific type of cancer, there are more factors added to the TNM categories for a better definition of a cancer stage:
- Grade: It is the depiction of how much cancer cells look like healthy cells when analysed under a microscope. It may be represented using the letter “G” along with a number from 0 to 4. A lower number is said to be “differentiated” or a “low-grade tumour,” while, a higher number is said to be “poorly differentiated” or a “high-grade tumour.”
- Tumour markers or biomarkers: Tumor markers, or biomarkers, that can be indicative of the severity of the diagnosed cancer, also are used to denote a particular stage of cancer.
- Tumour genetics: Based on genetic analysis, scientists can predict the chances and severity of cancer. This standard is, therefore, also clinically used.
Other staging systems
The TNM system is mainly used to describe cancers that form solid tumors, such as breast, colon, and lung cancers. However, doctors use other staging systems to classify other types of cancer, such as:
- Central nervous system tumours (brain tumours): Due to the different speed of spread of cancerous brain tumours, no single staging system exists for central nervous system tumours.
- Childhood cancers: The AJCC does not include childhood cancers in its staging system. Doctors stage most childhood cancers separately according to other staging systems that are often specific to the type of cancer.
- Cancers of the blood: The TNM system does not describe leukemia, lymphoma, or multiple myeloma since they usually do not form solid tumors. Each blood cancer has a unique staging system.
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