How is cancer staging determined?

There are a number of different staging methods used for cancers and the specific staging criteria varies among cancer types. According to the NCI, the common elements considered in most staging systems are as follows:

• Site of the primary tumor
  
• Tumor size and number of tumors
  
• Lymph node involvement (spread of cancer into lymph nodes)
  
• Cell type and tumor grade* (how closely the cancer cells resemble normal tissue cells)
• The presence or absence of metastasis

However, there are two main methods that form the basis for the more specific or individual cancer type staging. The TMN staging is used for most solid tumors while the Roman numeral or stage grouping method is used by some clinicians and researchers on almost all cancer types.

The following is how the NCI describes the TNM staging system:

1. The TNM system is based on the extent of the tumor (T), the extent of spread to the lymph nodes (N), and the presence of distant metastasis (M). A number is added to each letter to indicate the size or extent of the primary tumor and the extent of cancer spread (higher number means bigger tumor or more spread).


Primary tumor (T)
TX - Primary tumor cannot be evaluated
T0 - No evidence of primary tumor
Tis - Carcinoma in situ (CIS; abnormal cells are present but have not spread to neighboring tissue; although not cancer, CIS may become cancer and is sometimes called pre-invasive cancer)
T1, T2, T3, T4 - Size and/or extent of the primary tumor
2.


Regional lymph nodes (N)
NX - Regional lymph nodes cannot be evaluated
N0 - No regional lymph node involvement
N1, N2, N3 - Involvement of regional lymph nodes (number of lymph nodes and/or extent of spread)
3.


Distant metastasis (M)
MX - Distant metastasis cannot be evaluated
M0 - No distant metastasis
M1 - Distant metastasis is present

Consequently, a person's cancer could be listed as T1N2M0, meaning it is a small tumor (T1), but has spread to some regional lymph nodes (N2), and has no detected metastasis (M0).

The Roman numeral or stage grouping method is described by the NCI as follows:

Stage	Definition
Stage 0	Carcinoma in situ.
Stage I, Stage II, and Stage III	Higher numbers indicate more extensive disease: Larger tumor size and/or spread of the cancer beyond the organ in which it first developed to nearby lymph nodes and/or organs adjacent to the location of the primary tumor
Stage IV	The cancer has spread to another organ(s).

As mentioned above, variations of these staging methods exist. For example, some cancer registries use surveillance, epidemiology, and end results program (SEER) termed summary staging. SEER groups cancer cases into five main categories:

• In situ: Abnormal cells are present only in the layer of cells in which they developed.
• Localized: Cancer is limited to the organ in which it began, without evidence of spread.
• Regional: Cancer has spread beyond the primary site to nearby lymph nodes or organs and tissues.
• Distant: Cancer has spread from the primary site to distant organs or distant lymph nodes.
• Unknown: There is not enough information to determine the stage.

Staging of cancer is important; it helps the physician to decide on the most effective therapeutic protocols, provides a basis for estimating the prognosis (outcome) for the patient, and provides a system to communicate the patient's condition to other health professionals that become involved with the patients' care. 

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