Cancer staging means determining the degree to which the cancer has spread, and to what extent it involves other areas of the mouth and neck, or even distant parts of the body. Oral cancer stages are based on the results of physical exams, biopsies, and imaging tests.
The TNM classification system stages different types of cancer based on certain standard criteria:
T describes the size of the original (primary) tumor. N indicates whether or not the cancer has reached nearby lymph nodes. Lymph nodes are small clusters of immune system cells that are key to fighting infections and are one of the first sites in the body to which cancer spreads. M measures whether the cancer has spread (metastasized) to other areas of the body.
According to the TNM measurements and its various combinations, oral cancer is classified as stage 0, 1, 2, 3 or 4 cancer.
Tis, N0, M0 ("Carcinoma in situ")
The cancer is only growing in the epithelium (the outermost layer of tissue) in the oral cavity or oropharynx. It has not spread in deeper layers of tissue, nearby structures, lymph nodes, or other parts of the body.
T1, N0, M0
The primary oral cancer tumor is 2 cm across or smaller, it has not yet spread to lymph nodes or other parts of the body.
T2, N0, M0
The tumor measures 2–4 cm across, and the cancer has not yet spread to lymph nodes or other parts of the body.
T3, N0, M0 or T1–3, N1, M0
The cancer is larger than 4 cm and may or may not have reached one lymph node, which is located on the same side of the head or neck as the primary tumor. If a lymph node is affected it is smaller than 3 cm.
Stage IV describes various TNM combinations that are typical of "advanced" oral cancers with the primary cancer infiltrating surrounding tissues, spreading to lymph nodes and/or other parts of the body.
Below are a few examples:
T4, N1-3, M0
The primary cancer has invaded deeper areas and/or tissues. It may or may not have spread to lymph nodes but has not spread to other parts of the body.
T1–4, N2, M0
The tumor is any size and may or may not have invaded nearby structures and has not spread to other parts of the body, but has reached more than one lymph node or one lymph node located on the other side of the head or neck from the primary tumor (all lymph nodes measuring less than 6 cm across).
T1-3, N3, M0
The primary tumor is any size, may or may not have grown into other structures but has spread to one or more lymph nodes which are larger than 6 cm across. The tumor has not spread to other parts of the body.
T1-3, N1-3, M1
The oral cancer tumor is any size and may or may not have spread to lymph nodes. Cancer cells have spread to other parts of the body, most commonly the lungs, liver or bones.