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.
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.
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)
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
No regional lymph node involvement
N1, N2, N3: Degree of regional lymph node involvement (number and location of lymph nodes)
Distant Metastasis (M)
Distant metastasis cannot be evaluated
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 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
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 lymphomas. The Ann Arbor staging classification is commonly used to stage lymphomas and has been adopted by both the AJCC and the UICC. However, other cancers of the blood or bone marrow, including most types of leukemia, do not have a clear-cut staging system. Another staging system, developed by the International Federation of Gynecology and Obstetrics (FIGO), is used to stage cancers of the cervix, uterus, ovary, vagina, and vulva. This system is also based on TNM information. Additionally, most childhood cancers are staged using either the TNM system or the staging criteria of the Children’s Oncology Group (COG), which conducts pediatric clinical trials; however, other staging systems may be used for some childhood cancers.
Many cancer registries, such as those supported by NCI’s Surveillance, Epidemiology, and End Results (SEER) Program, use “summary staging.” This system is used for all types of cancer. It groups cancer cases into five main categories:
- In situ: Abnormal cells are present only in the layer of cells in which they developed
- Localized: Cancer is limited to the organ in which it began, without evidence of spread
- Regional: Cancer has spread beyond the primary site to nearby lymph nodes or tissues and organs
- Distant: Cancer has spread from the primary site to distant tissues or organs or to distant lymph nodes
- Unknown: There is not enough information to determine the stage
What types of tests are used to determine stage?
The types of tests used for staging depend on the type of cancer. Tests include the following:
- Physical exams are used to gather information about the cancer. The doctor examines the body by looking, feeling, and listening for anything unusual. The physical exam may show the location and size of the tumor(s) and the spread of the cancer to the lymph nodes and/or to other tissues and organs.
- Imaging studies produce pictures of areas inside the body. These studies are important tools in determining stage. Procedures such as x-rays, computed tomography (CT) scans, magnetic resonance imaging (MRI) scans, and positron emission tomography (PET) scans can show the location of the cancer, the size of the tumor, and whether the cancer has spread.
- Laboratory tests are studies of blood, urine, other fluids, and tissues taken from the body. For example, tests for liver function and tumor markers (substances sometimes found in increased amounts if cancer is present) can provide information about the cancer.
- Pathology reports may include information about the size of the tumor, the growth of the tumor into other tissues and organs, the type of cancer cells, and the grade of the tumor. A biopsy may be performed to provide information for the pathology report. Cytology reports also describe findings from the examination of cells in body fluids.
- Surgical reports tell what is found during surgery. These reports describe the size and appearance of the tumor and often include observations about lymph nodes and nearby organs.
Reference: National Cancer Institute (NCI)
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