The clinical stage of anal cancer is determined during diagnosis of the disease, which may include a physical exam, imaging tests and/or biopsy. Surgical or pathological staging (if surgery has been performed) is done by examining tissue.
The most commonly used anal cancer staging system is the TNM system established by the American Joint Committee on Cancer. The TNM staging system examines three key factors to determine the stage of cancer:
T (tumor): This describes the size of the original tumor.
N (node): This indicates whether the cancer is present in the lymph nodes.
M (metastasis): This refers to whether cancer has spread to other 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, one of the following overall anal cancer stage is assigned:
Stage 0: The cancer has not grown beyond the top layer of anal tissue and has not spread. Also called carcinoma in situ or Bowen’s disease.
Stage I (stage 1 anal cancer): The cancer has spread beyond the top layer of anal tissue, but it has not spread to nearby lymph nodes or distant sites. The tumor is less than 2 cm.
Stage II (stage 2 anal cancer): The tumor is greater than 2 cm but has not spread to nearby organs, lymph nodes or distant sites.
Stage III (stage 3 anal cancer): There are two subcategories of stage III anal cancer: IIIA and IIIB. The categories differ by the extent to which the cancer has spread.
Stage IV (stage 4 anal cancer): In this, the most advanced stage of anal cancer, the cancer is any size and may or may not have spread to nearby organs, such as the vagina or bladder. The cancer may or may not have spread to nearby lymph nodes. The cancer has spread to distant organs and tissues.
Next topic: How is anal cancer diagnosed?