Cancer Staging

Key Points

• Staging describes the extent or severity of a person’s cancer. Knowing the stage of disease helps the doctor plan treatment and estimate the person’s prognosis.
• Staging systems for cancer have evolved over time and continue to change as scientists learn more about cancer.
• The TNM staging system is based on the size and/or extent (reach) of the primary tumor (T), whether cancer cells have spread to nearby (regional) lymph nodes (N), and whether metastasis (M), or the spread of the cancer to other parts of the body, has occurred.
• Physical exams, imaging procedures, laboratory tests, pathology reports, and surgical reports provide information to determine the stage of a cancer.

1. What is staging?

   Staging describes the severity of a person’s cancer based on the size and/or extent (reach) of the original (primary) tumor and whether or not cancer has spread in the body. Staging is important for several reasons:
   • Staging helps the doctor plan the appropriate treatment.
   • Cancer stage can be used in estimating a person’s prognosis.
   • Knowing the stage of cancer is important in identifying clinical trials that may be a suitable treatment option for a patient.
   • Staging helps health care providers and researchers exchange information about patients; it also gives them a common terminology for evaluating the results of clinical trials and comparing the results of different trials.
   Staging is based on knowledge of the way cancer progresses. Cancer cells grow and divide without control or order, and they do not die when they should. As a result, they often form a mass of tissue called a tumor. As a tumor grows, it can invade nearby tissues and organs. Cancer cells can also break away from a tumor and enter the bloodstream or the lymphatic system. By moving through the bloodstream or lymphatic system, cancer cells can spread from the primary site to lymph nodes or to other organs, where they may form new tumors. The spread of cancer is called metastasis.

2. What are the common elements of staging systems?

   Staging systems for cancer have evolved over time. They continue to change as scientists learn more about cancer. Some staging systems cover many types of cancer; others focus on a particular type. The common elements considered in most staging systems are as follows:
   
   • Site of the primary tumor and the cell type (e.g., adenocarcinoma, squamous cell carcinoma)
   • Tumor size and/or extent (reach)
   • Regional lymph node involvement (the spread of cancer to nearby lymph nodes)
   • Number of tumors (the primary tumor and the presence of metastatic tumors, or metastases)
   • Tumor grade* (how closely the cancer cells and tissue resemble normal cells and tissue)
   *More information can be found in the NCI fact sheet Tumor Grade.

3. What is the TNM system?

   The TNM system is one of the most widely used cancer staging systems. This system has been accepted by the Union for International Cancer Control (UICC) and the American Joint Committee on Cancer (AJCC). Most medical facilities use the TNM system as their main method for cancer reporting.
   The TNM system is based on the size and/or extent (reach) of the primary tumor (T), the amount of spread to nearby lymph nodes (N), and the presence of metastasis (M) or secondary tumors formed by the spread of cancer cells to other parts of the body. A number is added to each letter to indicate the size and/or extent of the primary tumor and the degree of cancer spread.
   Primary Tumor (T)
   TX: Primary tumor cannot be evaluated
   T0: No evidence of primary tumor
   Tis: Carcinoma in situ (CIS; abnormal cells are present but have not spread to neighboring tissue; although not cancer, CIS may become cancer and is sometimes called preinvasive cancer)
   T1, T2, T3, T4: Size and/or extent of the primary tumor
   Regional Lymph Nodes (N)
   NX: Regional lymph nodes cannot be evaluated
   N0: No regional lymph node involvement
   N1, N2, N3: Degree of regional lymph node involvement (number and location of lymph nodes)
   Distant Metastasis (M)
   MX: Distant metastasis cannot be evaluated
   M0: No distant metastasis
   M1: Distant metastasis is present
   For example, breast cancer classified as T3 N2 M0 refers to a large tumor that has spread outside the breast to nearby lymph nodes but not to other parts of the body. Prostate cancer T2 N0 M0 means that the tumor is located only in the prostate and has not spread to the lymph nodes or any other part of the body.
   For many cancers, TNM combinations correspond to one of five stages. Criteria for stages differ for different types of cancer. For example, bladder cancer T3 N0 M0 is stage III, whereas colon cancer T3 N0 M0 is stage II.
   

   Stage	Definition
   Stage 0	Carcinoma in situ
   Stage I, Stage II, and Stage III	Higher numbers indicate more extensive disease: Larger tumor size and/or spread of the cancer beyond the organ in which it first developed to nearby lymph nodes and/or tissues or organs adjacent to the location of the primary tumor
   Stage IV	The cancer has spread to distant tissues or organs

   Question 6 describes sources of additional information about staging for specific types of cancer.

4. Are all cancers staged with TNM classifications?

   Most types of cancer have TNM designations, but some do not. For example, cancers of the brain and spinal cord are staged according to their cell type and grade. Different staging systems are also used for many cancers of the blood or bone marrow, such as lymp