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Staging is the process of describing the extent to which cancer has spread from the site of its origin. It is used to assess a patient's prognosis and to determine the choice of therapy. The stage of a cancer is determined by the size and location in the body of the primary tumor, and whether it has spread to other areas of the body.

Staging involves using the letters T, N and M to assess tumors by:

• the size of the primary tumor (T);
• the degree to which regional lymph nodes (N) are involved.

Lymph nodes are small organs located along the channels of the body's lymphatic system which store special cells that fight infection and other diseases); and the absence or presence of distant metastases (M) ‐ cancer that has spread from the original (primary) tumor to distant organs or distant lymph nodes.

Each of these is categories is further classified with a number 1 through 4 to give the total stage. Thus a T1‐N1‐M0 cancer would describe a T1 tumor, N1 lymph node involvement, and no metastases.

Once the T, N and M are determined, a "stage" of I, II, III or IV is assigned:

• Stage I cancers are small, localized and usually curable.
• Stage II and III cancers typically are locally advanced and/or have spread to local lymph nodes.
• Stage IV cancers usually are metastatic (have spread to distant parts of the body) and generally are considered inoperable.

The staging system for head and neck cancers is a bit complicated. Though the nodal and metastasis staging systems are the same for all the different anatomical regions of the head and neck, the tumor staging systems are different.

A description of the common nodal and metastasis staging systems and a table that shows how tumor stage and nodal/metastasis stages can be combined to approximate the overall stage of a patient, wherever the primary tumor is located.

Nodes
NX: Regional lymph nodes cannot be assessed.

N0: No evidence of regional lymph node metastasis.

N1: Metastasis in a single ipsilateral (same side) lymph node, 3 cm or less in size.

N2a: Metastasis in a single ipsilateral (same side) lymph node more than 3 cm but not more than 6 cm in greatest dimension.

N2b: Metastasis in multiple ipsilateral (same side) lymph nodes, none more than 6cm in greatest dimension.

N2c: Metastasis in bilateral (both) or contralateral (opposite side) lymph nodes, none more than 6 cm in greatest dimension.

N3: Metastasis in a lymph node more than 6 cm in greatest dimension.

Metastasis
MX: Presence of distant metastasis cannot be assessed.

M0: No evidence of distant metastasis.

M1: Distant metastasis present.

General Summary of Staging System

Note that for all Stages I through IVb, the metastasis stage is MX or M0. Regardless of tumor size or stage of lymph node involvement, the presence of distant metastasis automatically indicates Stage IVc.

Cancer that returns or develops again after all visible evidence of a tumor has been eradicated through treatment is called recurrent disease. Disease that recurs in the area of the original or primary tumor is called locally recurrent; that which recurs as metastases is referred to as a distant recurrence. Distant recurrence is usually treated as Stage IV disease.