The stage of cancer at the time of diagnosis is a critical piece of information that helps define a person’s overall prognosis as well as the most appropriate treatment options for that particular type of cancer.
At diagnosis, the stage of cancer is typically determined by a staging system developed by the American Joint Committee on Cancer (AJCC). Called the tumor node metastasis (TNM) system, it classifies and groups cancers by the extent of the primary tumor (T), whether or not the cancer has spread to nearby lymph nodes (N), and whether or not the cancer has spread or metastasized to other organs (M).
According to the AJCC’s Cancer Staging Handbook (7th Edition), the TNM system evaluates the cancer based on the following criteria:
- T Category
- The T component is defined by the size or contiguous extension of the primary tumor. The roles of the size component and the extent of contiguous spread in defining T are specifically defined for each cancer site.
- N Category
- The N component is defined by the absence, or presence and extent of cancer in the regional draining lymph nodes. Nodal involvement is categorized by the number of positive nodes and for certain cancer sites by the involvement of specific regional nodal groups.
- M Category
- The M component is defined by the absence or presence of distant spread or metastases, generally in locations to which the cancer spread by vascular channels, or by lymphatics beyond the nodes defined as 'regional.'
Each T, N and M category is then further defined by numbers (i.e., 1, 2, 3 or 4) that further showcase the extent of cancer. Following are the general designators for T, N, and M:
- Primary Tumor (T)
- T0: No evidence of primary tumor
- Tis: Carcinoma in situ
- T1, T2, T3, T4: Increasing size and/or local extension of the primary tumor
- TX: Primary tumor cannot be assessed
- Regional Lymph Nodes (N)
- N0: No regional lymph node metastases
- N1, N2, N3: Increasing number or extent of regional lymph node involvement
- NX: Regional lymph nodes cannot be assessed
- Distant Metastasis (M)
- M0: No distant metastasis
- M1: Distant metastasis present
Further subdivisions for some forms of cancer
Some forms of cancer, such as breast and prostate cancer, further subdivide the TNM designators (i.e., T1a, T1b, T1c or N2a, N2b). Additionally, some forms of cancer do not use the TNM system. For example, brain and spinal cord cancers are usually staged by their cell type and grade.
Other staging systems used for some cancers
Certain forms of blood and bone marrow cancer also use other staging systems. However, it is important to note that the AJCC TNM system is one of the most widely used cancer staging systems throughout the world.
