The TNM staging system is followed in the diagnosis of anal cancer. Anal cancer comprises five stages ranging from stage 0 (zero) and stages I to IV (1 to 4). The staging system has provided a general way to describe cancer so that doctors can work together to plan the best treatment. The experts have also explained anal cancer by grade (G). The grade represents the number of anal cancer cells that look like healthy cells under a microscope. The grading system ranges from GX to G4. In the case of recurrent anal cancer, tests are done to determine the extent of the recurrence.
Staging System of Anal Cancer
Staging is a way to explain where the cancer is, whether it has spread, where it has extended, and whether it impacts other parts of the body. Doctors use diagnostic tests to define the stages of anal cancer, so staging may not be complete until all tests have been completed. Knowing the stage helps doctors recommend the best treatment and predict the patient’s prognosis or chance of recovery. There is a different stage description for each type of cancer 1,2.
TNM staging system
One of the tools doctors use to explain the stage is the TNM system. Doctors use the outcomes of diagnostic tests and scans to answer the following questions:
- Tumor (T): What is the size of the primary tumor? Where is it?
- Lymph node (N): Did the tumor spread to the lymph nodes? If so, where and how many?
- Metastasis (M): Did cancer spread to other parts of the body? If so, where and how much?
Combine the results to determine the stage of each person’s cancer. Anal cancer has five stages: stage 0 (zero) and stages I to IV (1 to 4). The stage provides a general way to describe cancer so that doctors can work together to plan the best treatment.
The TNM system uses the letter “T” and a letter or number (0-4) to indicate the size and location of the tumor. Tumor size is measured in centimeters (cm). One centimeter is approximately the width of a commercially available ballpoint pen or pencil. The stage can also be divided into smaller groups to help explain the tumor in more detail. Here you will find various information about the stage of the tumor. TX: Primary tumor cannot be evaluated.
- T0: No tumor present. This Carcinoma in situ (cancer that has not previously spread to other tissues) is present.
- T1: Tumor is less than 2 centimeters (cm).
- T2: Tumor is more significant than 2 cm and less than 5 cm.
- T3: Tumor is more than 5 cm.
- T4: The tumor has invaded other organs such as the urethra, bladder, and vagina.
The “N” in the TNM staging system represents a lymph node. Lymph nodes are small bean-shaped organs that help fight infections. Lymph nodes near the anus are called local lymph nodes. Lymph nodes in different body parts are known as distant lymph nodes.
- NX: Local lymph nodes cannot be evaluated.
- N0 (N + zero): No local lymph node metastasis.
- N1: Cancer has spread to the groin (groin), perirectal (perirectal), internal iliac (pelvis), or external iliac lymph nodes.
- N1a: Cancer has spread to the groin (groin), perirectal (perirectal), or intrapelvic (pelvic) lymph nodes on the same side of the body.
- N1b: Anal Cancer has spread to the external pelvic (pelvic) lymph nodes
- N1c: Cancer has spread to the inguinal (groin), perirectal (perirectal) or internal pelvic (pelvic) lymph nodes, external Metastasized to pelvic lymph nodes.
The “M” in the TNM system indicates whether anal cancer has spread to other parts of the body called metastases.
- MX: Distant metastases cannot be evaluated.
- M0 (M plus zero): No distant metastasis.
- M1: There is metastasis to different parts of the body.
Doctors also describe anal cancer by grade (G). The grade represents the number of anal cancer cells that look like healthy cells under a microscope. Doctors compare cancerous and healthy tissue. Healthy tissues usually have different types of cells grouped. Cancer resembles a healthy tissue and a diverse group of cells; it is called a “differentiated” or “low-grade tumor.” When cancerous tissue differs significantly from healthy tissue, it is called “poorly differentiated” or “high-grade tumor”. The spite of cancer helps doctors predict how quickly cancer will spread. In general, the lower the malignancy of a tumor, the better the prognosis.
- GX: Tumor grade cannot be determined.
- G1: The cells look like normal histiocytes (well-differentiated).
- G2: Cells are slightly different from normal cells (middle differentiation).
- G3: Cells do not look like normal cells (poor differentiation).
- G4: The cells are very similar to normal cells (undifferentiated).
Anal Cancer stage grouping
Doctors combine T, N, and M to assign anal cancer stages. Doctors also include G. Stage 0: Abnormal cells are found only in the first layer of the anal mucosa. Abnormal cells can turn into cancer. This stage is also called Carcinoma in situ (Tis, N0, M0).
- Stage I: Tumor is less than 2 cm and has not spread to lymph nodes or other body parts (T1, N0, M0).
- Stage II: The tumor is more significant than 2 cm and has not spread to the lymph nodes or other body parts (T2 or T3, N0, M0).
- Stage IIIA: Tumors of any size have spread to nearby lymph nodes or organs such as the female urethra, bladder, vagina (T1 or T2, N1, M0, or T4, N0, M0).
- Stage IIIB: The tumor has invaded other nearby organs, but the spread of lymph nodes is limited to the area around the rectum. There is no long-distance distribution. Alternatively, the tumor can be of any size. Lymph node spread may be local or distant, but there is no spread of the disease to distant organs (T4, N1, M0; or T, N2 or N3, M0).
- Stage IV: Tumor is of any size and has spread to lymph nodes and distant body parts (any T, any N, M1).
Recurrent cancer shows the occurrence even after treatment. If Anal cancer has recurred, another test will be done to check the extent of the recurrence. Different tests and scans are often similar to those done at the time of the initial diagnosis.
- 1.Durot C, Dohan A, Boudiaf M, Servois V, Soyer P, Hoeffel C. Cancer of the Anal Canal: Diagnosis, Staging and Follow-Up with MRI. Korean J Radiol. 2017;18(6):946-956. doi:10.3348/kjr.2017.18.6.946
- 2.Matalon S, Mamon H, Fuchs C, et al. Anorectal Cancer: Critical Anatomic and Staging Distinctions That Affect Use of Radiation Therapy. Radiographics. 2015;35(7):2090-2107. doi:10.1148/rg.2015150037