Cancer Staging Guide
What is cancer staging?
If you have cancer, your doctors will want to know the extent of its growth. Cancer staging is a rating by your doctors of the extent of the cancer based on tests. Laboratory tests are often used to assess how much the cancer has grown within tissue removed from your body. Imaging tests may also be used for cancer staging. Imaging tests make pictures of the insides of your body. The pictures allow your doctors to see where the cancer has grown and spread.
More recently, information other than where and how much cancer is in your body is being used to stage some cancers. Such information may include blood test results, histologic (cell) test results, and risk factors. A risk factor is anything that increases your chances for a health event, such as fast cancer growth. However, where and how much cancer is in your body is still central to cancer staging.
Cancer staging is important for a few reasons. Often, your doctors will decide if you need more tests based on the cancer stage. The cancer stage is also one of the factors that doctors use to assess prognosis. Prognosis is a medical term for the expected pattern and outcome of a disease. Very importantly, the cancer stage is one factor used by your doctors to plan which treatments are best for you. As for research, the cancer stage is used to assess treatment results among patient groups, to compare results between treatment centers, and to plan research studies.
Cancer is often staged twice. The first rating is done before treatment and is called the clinical stage. The second rating is done after treatment, such as surgery, and is called the pathologic stage. The pathologic stage is more precise the extent of the cancer.
TNM staging system
The TNM staging system is most often used by doctors to stage cancer. It is maintained by AJCC (American Joint Committee on Cancer) and UICC (Union for International Cancer Control). In this system, the letters T, N, and M describe a different area of cancer growth. Based on test results, your doctors will assign a score to each letter. However, not all cancers, such as Hodgkin lymphoma, are rated by TNM scores.
T = Tumor
The T score is a rating of the extent of the primary tumor. The primary tumor is the first mass of cancer cells in the body. If not treated, the primary tumor can grow large. It can also grow through the layers of tissue in which it started. This is called tumor extension. Once the tumor has grown through the outer edge of a structure, it can grow into other nearby structures. This is called invasion.
T scores are based on the presence, size, and extension of the primary tumor. A TX score means that the primary tumor can’t be assessed. A T0 score means there is no primary tumor. It is possible to have cancer but not have a primary tumor. A Tis score means there are abnormal or cancer cells, but there is no chance for the cells to spread to distant sites. Scores of T1, T2, and so on are based on the primary tumor’s size, extension, or both. Higher values mean a greater extent of the cancer.
N = Nodes
The N category reflects the extent of cancer within nearby lymph nodes. Lymph nodes are small disease-fighting organs that filter lymph. Lymph is a clear fluid within tissue that gives cells water and food. It also collects waste from cells and has white blood cells that fight germs. Lymph drains from tissue into lymph vessels that transport it to the lymph nodes. Cancer cells can invade lymph vessels and travel to lymph nodes. Once in lymph nodes, the cancer cells can multiply and form new tumors.
N scores are based on whether there’s cancer in nearby lymph nodes and the number or region of nodes with cancer. A NX score means that the lymph nodes can’t be assessed. A N0 score means that no cancer was found in the lymph nodes. N1, N2, and N3 scores are based on the number of nodes with cancer or which nodal groups have cancer. Higher values mean a greater extent of the cancer.
M = Metastasis
The M category tells you if the cancer has spread to distant sites. Such sites include distant lymph nodes beyond nearby lymph nodes. Cancer cells can break off the primary tumor and spread to distant sites. This process is called metastasis. Cancer cells can spread to distant sites through lymph or blood. M0 means there is no cancer in distant sites. M1 means there is cancer in distant sites.
Each type of cancer has its own stage groups based on where the cancer has grown and spread. There are either four or five stage groups per cancer. Stage groups are ranked by Roman numerals starting with either stage 0 or stage I and end at stage IV.
Stage groups for most cancers are defined by TNM scores. If TNM scores aren’t used, stage group are still defined by where the cancer is in the body. Some cancers that are grouped by TNM scores also use other information to define the stage groups.
All people who meet the criteria of a stage group have a similar prognosis. In general, earlier cancer stages have better outcomes. However, doctors define cancer stages with information from thousands of patients, so a cancer stage gives an average outcome. It may not tell the outcome for one person. Some people will do better than expected. Others will do worse.
Cancers that can’t spread to distant sites are rated as stage 0. Stage I includes small primary tumors that haven’t spread to lymph nodes. Stage II and III are larger or more extensive primary tumors with or without cancer in nearby lymph nodes. Stage IV is cancer that has spread to distant sites at diagnosis.