TNM System for anal cancer
The most commonly used anal cancer staging system is the TNM system established by the American Joint Committee on Cancer. The TNM staging system looks at three key factors to determine the stage of cancer:
- Tumor (T) describes the number and size of the original tumor.
- Lymph Node (N) indicates whether the cancer is present in the regional (nearby) lymph nodes.
- Metastasis (M) refers to whether cancer has spread to distant parts of the body.
A number (0-4) or the letter X is assigned to each factor. A higher number indicates increasing severity. For instance, a T1 score indicates a smaller tumor than a T2 score. The letter X means the information could not be assessed.
Once the T, N and M scores have been assigned, an overall anal cancer stage is assigned.
Primary tumor (T)
The primary tumor can be categorized as T0 to T4 for anal cancer. Below is a description of how tumors are defined using the TNM staging system.
TX: The primary tumor cannot be assessed.
T0: There is no evidence of a primary tumor.
Tis (carcinoma in situ): In situ means that the cancer is in the earliest stage and has not grown beyond the lining of rectum.
T1: The tumor is 2 cm or less.
T2: The tumor is between 2 cm and 5 cm.
T3: The tumor is greater than 5 cm.
T4: A tumor of any size invades nearby organs, such as the vagina, urethra and bladder.
Regional lymph nodes (N)
NX: Regional lymph nodes cannot be assessed.
N0: The cancer has not spread into the lymph nodes.
N1: The cancer has spread to perirectal lymph nodes.
N2: The cancer has spread to unilateral internal iliac and/or inguinal lymph nodes.
N3: The cancer has spread to perirectal and inguinal and/or bilateral internal iliac and/or inguinal lymph nodes.
Distant metastasis (M)
M0: The cancer has not spread to distant organs.
M1: The cancer has spread to distant organs.