Cancer : Detailed Guide

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The TNM Staging System

At one time there were many different systems used to stage cancers, and sometimes different systems were used to stage the same type of cancer. Although some of the better ones are still used, many of these systems did not give doctors very useful information.

The American Joint Committee on Cancer (AJCC) developed the TNM classification system as a tool for doctors to stage different types of cancer based on certain standard criteria. It has replaced many of the older staging systems. In the TNM system, each cancer is assigned a T, N, and M category.

The Tcategory describes the original (primary) tumor. The tumor size is usually measured in centimeters (2 and 1/2 centimeters is about 1 inch) or millimeters (10 millimeters = 1 centimeter.)
* TX means the tumor can't be measured or evaluated.
* T0 means there is no evidence of primary tumor (the primary tumor cannot be found).
* Tis means the cancer is in situ (the tumor has not started growing into the structures around it).
* The numbers T1–T4 describe the tumor size and/or level of invasion into nearby structures. The higher the T number, the larger the tumor and/or the further it has grown into nearby structures.

The N category describes whether or not the cancer has reached nearby lymph nodes.
* NX means the nearby lymph nodes can't be measured or evaluated.
* N0 means nearby lymph nodes do not contain cancer.
*The numbers N1–N3 describe the size, location, and/or the number of lymph nodes involved. The higher the N number, the more lymph nodes are involved.

The M category tells whether there are distant metastases (spread of cancer to other parts of body).
* MX means metastasis can't be measured or evaluated.
* M0 means that no distant metastases were found.
* M1 means that distant metastases were found (the cancer had spread to distant organs or tissues.)

Each cancer type has its own version of this classification system, so letters and numbers don't always mean the same thing for every kind of cancer. For example, for some cancers, classifications may have subcategories, such as T3a and T3b, while others may not have an N3 category.

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