The colon and rectum are part of the large intestine (large bowel). Colon and rectum cancers, which are sometimes referred to together as "colorectal cancer," arise from the lining of the large intestine. (When cancer arises from the lining of an organ like the large intestine, it is called a carcinoma.)

There is no single cause of colon cancer. However, almost all colon cancers begin as benign polyps which, over a period of many years, develop into cancers.

Factors that increase the risk of colon cancer are colorectal polyps, cancer elsewhere in the body, a family history of colon cancer, and ulcerative colitis.

Patients with a history of breast cancer have a slightly increased risk of developing colon cancer. Certain genetic syndromes predispose to the development of colon cancer in affected families.

Dietary factors that have been associated with colon cancer are a high-meat, high-fat, low-fiber diet. However, some studies have not supported a reduction in risk of colon cancer with a high fiber diet.

There are over 130,000 cases of colorectal cancer diagnosed in the United States each year. Colorectal cancer is the second leading cause of cancer deaths. This disease, however, in almost all cases, is entirely preventable.

• Diarrhea, constipation or other change in bowel habits that does not resolve.
• Blood in the stool
• Unexplained anemia (anemia in any adults other than menstruating women should almost always be evaluated by a colonoscopy)
• Abdominal pain and tenderness in the lower abdomen
• Intestinal obstruction
• Weight loss with no known reason
• Stools narrower than usual

Physical examination rarely shows abnormalities though an abdominal mass may be present. A rectal examination may reveal a mass in patients with rectal cancer, but not colon cancer.

A colonoscopy or sigmoidoscopy may reveal evidence of cancer. However only colonoscopy (NOT sigmoidoscopy) examines the entire colon.

A fecal occult blood test (FOBT) may detect small amounts of blood in the stool, a possible indicator of colon cancer. However, this test is often negative in patients with colon cancer. Not all polyps bleed, and not all polyps bleed all the time. That is why a FOBT must be used with one of the other more invasive screening measures (e.g., colonoscopy or sigmoidoscopy). Finally, a positive FOBT doesn't necessarily mean the person has cancer -- "false positives" can be caused by some medications and other factors.

A blood count may reveal evidence of anemia with low iron levels. CT scan may show an abdominal mass though this test is not very good at detecting colon cancer.

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 with a local exicision of 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 quality of life. Irinotecan and 5-fluorouracil are the two most commonly used drugs, given either individually or in combination. A new drug, oxaliplatin, is also useful in these patients, but has not yet been approved by the FDA.

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

Stage I, II, and III cancers are considered curable, based on the chance of living at least 5 years after diagnosis. In most cases, stage IV cancer is incurable.

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 IVdisease rarely live greater than five years and the average, or median survival, with treatment is betwen 1 and 2 years. Colon cancer rarely recurs after 5 years, thus most patients who live 5 years are considered cured.

• Metastasis to other organs or tissues
• Recurrence of carcinoma within the colon
• Development of second primary colorectal cancer

Colon cancer is, in almost all cases, a preventable disease. Removal of premalignant polyps by colonoscopy 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.

Approximately 50,000 people die of colon cancer every year, and yet, colon cancer is almost always preventable (or caught in its earliest, and most curable stages) by colonosocopy. Almost all men and women age 50 and older should have a colonoscopy.

Colonoscopy is almost always painless and most patients are asleep for the entire procedure. Taking laxatives and/or enemas before the test to clean out the colon isn't fun, but most people find this to be the worst part of the procedure. It may be embarrassing or awkward, but it is certainly better than having cancer.

Certain people may require colonoscopies at an age younger than age 50. These include persons with a history of colon polyps or a history of inflammatory bowel disease, and people with a first degree relative (mother, father, brother or sister) with colon cancer that developed before the age of 60.

Additionally, patients with personal or family history of other types of cancer may need to consider colon cancer screening at an earlier age.

Fecal Occult Blood Test, sigmoidoscopy, and barium enema are other screening tests that can be used for early detection and prevention of colon cancer, but colonoscopy remains the gold standard.

A new test, a virtual colonoscopy, uses CT scan technology to visualize the colon. There are several problems with this test, however. First, it is early in development and we still don't have enough information to determine how accurate it really is. Second, patients still must take a preparation the night before to clean out the colon. Finally, if an abnormality is seen, the patient must still undergo a traditional colonoscopy.

Dietary and lifestyle modifications are important. Some evidence suggests that low fat and high fiber diets may decrease the incidence of colon cancer. However, even patients who follow strict diets can still develop this disease and require colonoscopy.

Some evidence suggests that non-steroidal anti-inflammatory drugs (such as ibrupofen) may help prevent colon cancer, but again, screening is still necessary.