Treatment depends partly on the "stage" of the cancer. This means how far the tumor has spread through the layers of the intestine, from the innermost lining to outside the intestinal wall and beyond:

• Stage 0: Very early cancer on the innermost layer (more accurately considered a precursor to cancer)
• Stage I: Tumor in the inner layers of the colon
• Stage II: Tumor has spread through the muscle wall of the colon
• Stage III: Tumor that has spread to the lymph nodes
• Stage IV: Tumor that has spread to distant organs

Stage 0 colon cancer may be treated by cutting out the lesion, often via a colonoscopy. In some cases, more extensive surgery may be needed (see stages I-III). For stages I, II, and III cancer, removal of a segment of colon containing the tumor and reattachment of the colon is necessary. This procedure only rarely requires a colostomy.

Almost all patients with stage III colon cancer, after surgery, should receive chemotherapy (adjuvant chemotherapy) with a drug known as 5-fluorouracil given for approximately 8 months. This drug has been shown to increase the chance of being cured. There is some debate as to whether patients with stage II colon cancer should receive chemotherapy after surgery, and patients should discuss this with their oncologist.

Chemotherapy is also used for patients with stage IV disease in order to shrink the tumor, lengthen life, and improve the patient's quality of life. Irinotecan and 5-fluorouracil are the two most commonly used drugs, given either individually or in combination. There are oral chemotherapy drugs which are similar to 5-fluroruracil, the most commonly used being capecitabine (Xeloda).

Oxaliplatin, a newer chemotherapy drug, was approved by the FDA in 2002 and is also active against colon cancer. It is often used in combination with 5-fluorouracil, and studies are being done that combine it with other chemotherapy drugs. Other chemotherapy agents, including drugs that specifically target abnormalities in cancer cells, are currently in development and undergoing clinical trials.

For patients with stage IV disease that is localized to the liver, various treatments directed specifically at the liver can be used. Tumors can be surgically removed, burned, or frozen in some cases. Chemotherapy or radioactive substances can sometimes be infused directly into the liver.

Radiation therapy is occasionally used in patients with colon cancer, but this is relatively uncommon.

If the patient's colon cancer does not come back (recur) within 5 years, it is considered cured. This is because colon cancer rarely comes back after 5 years. Stage I, II, and III cancers are considered potentially curable. In most cases, stage IV cancer is not curable.

Stage I has a 90% 5-year survival. Stage II has a 75-85% 5-year survival, and Stage III a 40-60% 5-year survival. These numbers take into account that for stage III patients (and in some studies, stage II patients) chemotherapy improves the chance of 5-year survival.

Patients with stage IV disease rarely live beyond five years and the median survival (meaning half the patients live longer, and half shorter) with treatment is between 1 and 2 years.

• Cancer spreading to other organs or tissues (metastasis)
• Recurrence of carcinoma within the colon
• Development of a second primary colorectal cancer

Colon cancer is, in almost all cases, a treatable disease if caught early. Removal of premalignant polyps by colonoscopy essentially prevents colon cancer. Any man or woman age 50 or over who has not had a colonoscopy should call his or her physician to schedule one.

Additionally, call your physician if you develop blood in the stool (either visible blood or blood detected by a home fecal occult blood test), black tarry stool, or a change in bowel habits. However, it is important to emphasize that most people with colon cancer have no symptoms.