Staging usually occurs before cancer treatment is decided. The staging system helps the surgeon to decide the prognosis and to select the best treatment plan for each individual patient.
To stage a cancer, a pathologist examines the tumor cells under a microscope and describes the cells. A computed tomography (CT) scan , magnetic resonance imaging (MRI) or positron emission tomography (PET) scan helps determine if the tumor has spread to the lymph nodes or other organs. The pathology description, and the result of the scans, helps the doctor determine the stage.
The American Joint Committee for Cancer (AJCC) and the International Union Against Cancer (UICC) have agreed on a method to describe the stage of a cancer. This is called the TNM system:
T is for tumor
N is for node
M is for metastasis (has spread to other organs)
A number from 0-4 is assigned to each letter, such as T1 N1 M0. The number describes the size of the tumor: 0 is the smallest size and 4 is the largest.
Some N (node) categories have sub-categories that use the small case letters a, b, or c. Small case letters describe the extension of cancer:
a means cancer is in the lymph nodes
b means cancer is on one side only
c means cancer is on both sides
A sub-category tumor stage might be described as T2 N2a M0.
TNM is confusing. It is not necessary to know the exact meaning of each letter and number, but a basic knowledge is helpful. Your doctor will explain the stage of the tumor and the best treatment for you.