Colon cancer most commonly spreads to local lymph nodes and the liver. The TNM system, along with staging from 0 to IV, is used to classify the malignancy and degree of metastasis of cancer. People who have tumors in their ascending or rectosigmoid colon do better than those with tumors in the transverse and descending colon.

In the TNM system (an abbreviation for tumor, node and metastases), T0 means no disease, T1 and T2 indicate tumors that have not spread, and T3 and T4 reflect more advanced cancer.

In colon cancer, T1 disease has entered only the layer of tissue underneath the lining of the colon, called the submucosa. T2 disease has entered a deeper layer called the muscularis propria; T3 has passed through the muscularus propria and T4 disease has invaded other organs or perforated the layer of tissue surrounding the abdominal organs, which is called the abdominal viscera.

The "N" in the system indicates whether the cancer has spread to lymph nodes (tiny organs of the immune system located throughout the body), and the "M" indicates whether the cancer has spread to other parts of the body. N0 means lymph nodes aren't affected; in N1 disease the cancer has spread to one to three regional lymph nodes; N2 disease has spread to four or more regional lymph nodes; and N4 disease affects regional lymph nodes near an important blood vessel. M0 indicates that the disease has not spread, or metastasized, while M1 denotes metastasis.

The Stage 0-IV system is as follows:

Stage 0:Carcinoma in situ (CIS), abnormal tissue that has not spread beyond its original site. Treated by removing polyp.

Stage I: Tumors are T1 or T2 with no lymph node involvement (N0) and no metastases (M0). Treated with surgery. Five-year survival is 85 to 95 percent.

Stage II: Tumors are T3 or T4 with no lymph node involvement (N0) or metastases (M0). Treated with surgery. Patient may enter clinical trial of biological therapy, chemotherapy or radiation. Five-year survival is 60 to 80 percent.

Stage III: Tumors of any classification with lymph node involvement (N1-N2) but no metastases (M0). Treated with surgery and chemotherapy with 5-FU and leukovorin. Patient may enter clinical trials of chemotherapy, radiation or biological therapy. Five-year survival is 30 to 60 percent.

Stage IV: Tumors of any classification with lymph node involvement (N2-N4) and distant metastases (M1). Treated with surgery to remove primary tumor and metastases, and chemotherapy, radiation and clinical trials. Five-year survival is less than 5 percent.