The gastrointestinal (GI) tract begins at the mouth, traverses through the body, and exits at the anus. It comprises the esophagus traversing through the chest and nearly all major abdominal organs, namely the stomach, intestines, liver, biliary tract, gallbladder, pancreas, appendix, and rectum.

Common GI problems and symptoms that bring people to see doctors include food poisoning, nausea, vomiting, passing blood, jaundice, heartburn, indigestion, bloating, abdominal pain, and constipation. If the symptoms are recurrent or cause significant discomfort, do not hesitate to see a doctor. Most gastrointestinal diseases are preventable, and early detection can lead to better outcomes.

GI symptoms may or may not be related to cancer. For example, if you see bright red blood in the toilet bowl or when you wipe, it could come from hemorrhoids or colorectal cancer (CRC).

Almost all CRCs begin as a polyp, benign (non-cancerous) growths in the lining of your colon or rectum. Colonic polyps are usually asymptomatic, but they may induce tenesmus, ulcerate, and bleed. Cancer develops when these polyps grow, some cells become cancerous and start to invade surrounding tissue. In Thailand, CRC has now risen to be the fourth most common cancer behind liver, lung, and breast cancers, with more than 11,000 new cases per year.

One distinct characteristic of CRC is that it has a long duration existing as benign polyp before turning malignant through a multi-step process. This affords ample opportunity to preempt the development of cancer if the polyp is removed at this stage. Because most polyps and early stage CRCs do not cause symptoms, a colon cancer screening test should begin while you are asymptomatic. Once symptomatic, the cancer usually has progressed to late stages invading through the colonic wall and may have spread to lymph nodes, liver, and lungs. Aggressive types of cancer have a faster disease progression.

Growth of the cancer into the colonic lumen and adjacent structures causes symptoms including blood on or mixed in with the stool, change in bowel habits, pencil-thin stools, abdominal pain, weight loss, or constant fatigue.

The following risk factors increase your chances of having colon cancer:

• A diet high in red, processed, or grilled and charred meat
• Obesity, particularly those with excess abdominal visceral fat.
• Smoking
• Drinking too much alcohol
• Age is a major risk factor, increasing significantly between and after the ages of 40 and 50
• Family history of CRC in a first degree relative

CRC can be easily cured if found and treated in its early stages. One of the most effective ways to detect colorectal cancer is colonoscopy. The colonoscope, fitted with a tiny video camera and a light source at its tip, allows doctors to inspect the internal lining of the entire colon. If a suspicious lesion is found, a special instrument can be inserted through a small channel in the endoscope to take tissue samples (biopsies). If a polyp is found, it can be removed in the same sitting. Most polyps rest on a thin stalk and could be easily removed with an electric thin wire loop snare, literally nipping cancer in the bud. The procedure typically lasts about 30-60 minutes. It is done under moderate sedation; you will sleep through the procedure without feeling any discomfort.

A colonoscopy is recommended for:

• Investigating intestinal signs and symptoms: As diagnostic procedure to delineate the causes of abdominal pain, rectal bleeding, chronic diarrhea, and other intestinal problems.
• Screening for colon cancer: Adults with an average risk of CRC beginning at age 45 or sooner in high risk groups.
• Looking for more polyps: Periodic follow-up colonoscopy is recommended for patients who have had polyps removed previously. New polyps, if found could be removed, forestalling CRC development.
• Treating a clinical condition: Sometimes, a colonoscopy may be done for therapeutic purposes.

You need to clean out your colon in preparation for colonoscopy. Any retained feces in the colon make it difficult to get a good view of your colon and rectum and may obscure a lesion.

To empty your colon, your doctor may ask you to:

• Follow a special diet the day before the exam. Typically, you won't be able to eat solid food the day before the exam. Fluid intake may be limited to clear liquids.
• Take a laxative. Your doctor will usually prescribe a laxative, usually in large volumes (2-4 L).
• Adjust your medications. Notify your doctor of your usual medications at least a week before the exam; certain medications may need to be temporarily withheld.

It takes about an hour to recover from the sedative given for the colonoscopic procedure. You should not drive during the first 24 hours; have someone to take you home because it can take up to a full day for the sedative to completely wear off. You may feel bloated or pass gas for a few hours after the exam as your bowel expels residual gas insufflated into the colon during the procedure. Walking may help relieve any bowel discomfort. If your doctor removes a polyp during the colonoscopy, you may be advised to temporarily follow a special diet.

Things you can do to prevent GI problems and lower the risk of developing CRC.

• Avoid excessive caffeine and monitor which foods trigger your GI symptoms.
• Add more fruits, vegetables, and fiber to your diet and eat less animal meat and fat.
• Exercise regularly, even moderate regular physical activity is beneficial.
• Maintain a healthy weight. Obesity is an important risk factor for colon cancer.

However, these may not be sufficient to entirely prevent CRC; thus a colonoscopy for CRC screening is necessary, particularly when you turn 45.

Through colonoscopy, it is possible to prevent, detect and treat the disease long before symptoms appear. Almost all precancerous polyps can be removed painlessly through a colonoscope. Colonoscopy can detect any abnormal mucosal lesions in the colon such as polyps, mass, ulcer, colitis, diverticulum, abnormal vessels, and infection/inflammation.  An early stage CRC can also be completely removed by endoscopic techniques. If not caught in the early stages, CRC can spread throughout the body. Advanced cancer requires more complicated surgical operations and medical therapy. Patients diagnosed at a localized or early stage have a much higher chance for cure compared with those present with late stage cancer or metastatic spread at the time of diagnosis. Early detection gives the best chance for cure which can be achieved with a timely screening colonoscopy.