Staging is a way of describing where the cancer is located, if or where it has spread, and whether it is affecting other parts of the body. Doctors use diagnostic tests to find out the cancer’s stage, so staging may not be complete until all of the tests are finished.
Knowing the stage helps the doctor to decide what kind of treatment is best and can help predict a patient’s prognosis, which is the chance of recovery.
There are different stage descriptions for different types of cancer.
TNM staging system
One tool that doctors use to describe the stage is the TNM system. Doctors use the results from diagnostic tests and scans to answer these questions:
- Tumor (T): How large is the primary tumor? Where is it located?
- Node (N): Has the tumor spread to the lymph nodes? If so, where and how many?
- Metastasis (M): Has the cancer metastasized to other parts of the body? If so, where and how much?
The results are combined to determine the stage of cancer for each person. There are 5 stages of anal cancer: stage 0 (zero) and stages I through IV (1 through 4). The stage provides a common way of describing the cancer, so doctors can work together to plan the best treatments.
Here are more details on each part of the TNM system for anal cancer:
Using the TNM system, the “T” plus a letter or number (0 to 4) is used to describe the size and location of the tumor. Some stages are also divided into smaller groups that help describe the tumor in even more detail. Specific tumor stage information is listed below:
T0: There is no tumor.
Tis: Carcinoma in situ (early cancer that has not spread to other tissue) is present.
T1: The tumor is no larger than 2 centimeters (cm).
T2: The tumor is larger than 2 cm but not larger than 5 cm.
T3: The tumor is larger than 5 cm.
T4: The tumor has invaded other organs, such as the urethra, bladder, or a woman’s vagina.
The “N” in the TNM staging system stands for lymph nodes, the tiny, bean-shaped organs that help fight infection. Lymph nodes near the anus are called regional lymph nodes. Lymph nodes in other parts of the body are called distant lymph nodes.
NX: Regional lymph nodes cannot be evaluated.
N0 (N plus zero): There is no regional lymph node metastasis.
N1: Cancer had spread to the perirectal (around the rectum) lymph nodes.
N2: Cancer has spread to the internal iliac (pelvic) and/or the inguinal (groin) lymph nodes on the same side of the body.
N3: Cancer had spread to the perirectal and inguinal lymph nodes and/or the internal iliac and/or inguinal lymph nodes on both sides of the body.
The “M” in the TNM system indicates whether the cancer has spread to other parts of the body, called distant metastasis.
MX: Distant metastasis cannot be evaluated.
M0 (M plus zero): There is no distant metastasis.
M1: There is metastasis to other parts of the body.
Doctors also describe this type of cancer by its grade (G), which describes how much cancer cells look like healthy cells when viewed under a microscope. The doctor compares the cancerous tissue with healthy tissue. Healthy tissue usually contains many different types of cells grouped together.
If the cancer looks similar to healthy tissue and contains different cell groupings, it is called differentiated or a low-grade tumor. If the cancerous tissue looks very different from healthy tissue, it is called poorly differentiated or a high-grade tumor.
GX: The tumor grade cannot be identified.
G1: The cells look more like normal tissue cells (well differentiated).
G2: The cells are somewhat different from normal cells (moderately differentiated).
G3: The cells do not look like normal cells (poorly differentiated).
G4: The cells barely resemble normal cells (undifferentiated).
Cancer stage grouping
Doctors assign the stage of the cancer by combining the T, N, M. The doctor will also include G as well.
Stage 0: Abnormal cells are in the first layer of the lining of the anus only. The abnormal cells may become cancer. This stage is also called carcinoma in situ (Tis, N0, M0).
Stage I: The tumor is no larger than 2 cm and has not spread to the lymph nodes or other parts of the body (T1, N0, M0).
Stage II: The tumor is larger than 2 cm and has not spread to the lymph nodes or other parts of the body (T2 or T3, N0, M0).
Stage IIIA: The tumor may be any size and has spread to either the nearby lymph nodes or to organs, such as the urethra, bladder, or a woman’s vagina (T1 or T2 or T3, N1, M0; or T4, N0, M0).
Stage IIIB: The tumor has invaded other nearby organs, but lymph node spread is limited to the area around the rectum; there is no distant spread. Or, the tumor may be of any size; lymph node spread can be local or distant, but there is no disease spread to distant organs (T4, N1, M0; or any T, N2 or N3, M0).
Stage IV: The tumor may be any size and has spread to the lymph nodes and to distant parts of the body (any T, any N, M1).
Recurrent: Recurrent cancer is cancer that has come back after treatment. If the cancer does return, there will be another round of tests to learn about the extent of the recurrence. These tests and scans are often similar to those done at the time of the original diagnosis.