Cancer develops when abnormal cells in the body grow out of control and fail to die when they should. These abnormal cells can grow into clumps known as tumors.
Cancer staging is the process used by doctors to determine how much cancer is in the body and where it is located. Knowing the stage of cancer is important to help doctors determine the best course of treatment.
Knowing the cancer stage also helps the doctors estimate a patient’s prognosis, which is the most likely outcome including the chance of recovery or having the cancer come back.
In general, cancer is given a designation of stage 1, stage 2, stage 3, or stage 4. The higher the number, the more the cancer has grown and the worse the prognosis will be.
Cancer is staged using one of several staging systems. Some systems are used to describe a particular type of cancer, such as prostate cancer. Blood cancers such as leukemia do not have a clear staging system.
Cancer staging systems continue to be refined as researchers learn more about cancer and how it grows.
The TNM system is one of the most commonly used cancer staging systems.
• T stands for the tumor, including size and number of tumors found.
• N stands for lymph nodes, which are collection areas for lymphatic fluid. This fluid is part of the immune system that helps filter cancer cells and bacteria out of the body.
• M stands for metastasis. When cancer cells break away from the initial tumor, they can travel through the blood or the lymph system to other parts of the body and form new tumors. These tumors are called metastases. The number of metastases is significant in staging cancer.
In each of these cases, the doctor will determine a rating for each element of the TNM system.
• TX means the primary tumor cannot be evaluated.
• T0 means there is no sign of a primary tumor.
• Tis means carcinoma in situ (CIS) which is an indication that there are abnormal cells present but they have not spread into surrounding tissue. CIS is not cancer, but is often considered to be a “pre-cancer” which often becomes cancer.