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Staging is a method used by doctors to determine how far the cancer has spread in the body. Staging is also important for guiding treatment and for predicting the prognosis (outcome) for the disease.

The important aspects of staging colorectal cancer are the depth of tumor invasion through the bowel wall, the extent of lymph node involvement in the region, and the presence or absence of distant spread of the cancer (metastases).

• Stages of Colon Cancer

  • Stage 0: Very early cancer that is confined to the innermost layer of the colon (also called carcinoma in situ).
  • Stage I: Cancer has grown into the deeper layers of the colon but has not spread outside the wall of the colon.
  • Stage II: Cancer has spread through the wall of the colon but has not yet spread to regional (nearby) lymph nodes.
  • Stage III: Cancer has spread through the wall of the colon to the regional lymph nodes but has not yet spread to distant organs.
  • Stage IV: Most advanced stage of colon cancer where the cancer has spread to distant organs such as the liver or lungs.

• Stages of Rectal Cancer

  • Stage 0: Very early cancer that is confined to the innermost layer of the rectum (also called carcinoma in situ).
  • Stage I: Cancer has grown into the deeper layers of the rectum but has not spread outside the wall of the rectum.
  • Stage II: Cancer has spread through the wall of the rectum but has not yet spread to regional (nearby) lymph nodes.
  • Stage III: Cancer has spread through the wall of the rectum to the regional lymph nodes but has not yet spread to distant organs.
  • Stage IV: Most advanced stage of rectal cancer where the cancer has spread to distant organs such as the liver or lungs.

TNM Classification System

The tumor-node-metastasis (TNM) system is the most commonly used system for staging colorectal cancer and also helps to predict survival rates.

• T = Tumor - The "T" designation refers to the extent of invasion of the tumor at the site of primary occurrence and into nearby tissue and other organs. The extent of tumor invasion is scored on a numerical scale ranging from 1 to 4. In general, the higher the "T" score, the greater the extent of invasion of the tumor into the deeper layers of tissue.

• N = Lymph Node Involvement - The second aspect of the TNM staging system measures whether or not the cancer has spread to the regional (nearby) lymph nodes and, if so, the size of the lymph nodes. The extent and size of lymph node involvement is scored on a numerical scale ranging from 0 to 2. In general, the higher the "N" score, the greater the extent of lymph node involvement.

• M = Metastasis - The last feature that is evaluated by the TNM staging system is whether or not the cancer has metastasized (spread) to distant organs (e.g., liver, lungs, abdominal cavity, pelvis, bladder) or to distant lymph nodes.

Tumor remaining after primary surgical resection is not evaluated by the TNM System, but is categorized by the "R" Classification: