The digestive system is made up of the esophagus (food pipe), stomach,and the small and large intestines. The upper 5 - 6 ft (1.5-1.8 m) of the large intestine is called the colon, and the last 6 - 8 in (15-20 cm) of the colon is the rectum. Colorectal cancer is a disease in which the cells of the tissues lining the colon and the rectum start to grow uncontrollably and formtumors.
The main function of the colon is to absorb water and the nutrients from thefood already digested by the stomach and the small intestine. The waste material left behind goes into the rectum. From here, it is excreted out of the body through the anus. The colon has four sections: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon which extends tothe rectum. Cancer can develop in any of the four sections or in the rectum (the last part of the colon). Cancers beginning in the different sections havedifferent symptoms.
Colorectal cancers have a very high cure rate if found early. Unfortunately,most colorectal cancers are "silent tumors." They grow slowly and often do not produce symptoms until they reach a large size. Therefore, diagnosis is often delayed. The cancer usually begins as a benign growth in the lining of theintestine. These benign growths are called polyps. There are two kinds of polyps, hyperplastic polyps that are small and completely benign. They do not ever develop into cancers. The second kind of polyps, called adenomas, are dangerous and have the potential to become cancerous.
While we do not know the exact cause of most colorectal cancers, the risk factors that makes a person more susceptible to colorectal cancer are:
- Family history: Some rare disease conditions such as Familial Adenomatous Polyps (FAP) and Lynch syndrome (a genetic condition that predisposes certain families to colon cancer. These may make an individual more likely to develop cancer of the colon or the rectum. Inheriting defective genes causes approximately 10% of colorectal cancers.
- History of colorectal cancer: Even when colorectal cancer has been completely removed, new cancers may still develop in other areas of the colon and the rectum.
- Recurrent intestinal polyps: Polyps are benign growths in the colon or rectum. While most polyps areharmless, some particular types do increase the risk of colorectal cancer, especially if they are large and there are many of them.
- Inflammatorybowel disease: Chronic ulcerative colitis, a condition in which the colon isinflamed over a long period of time and causes ulcers in the lining, can increase the risk of colon cancer.
- Age: About 90% of colorectal cancersare found in people over the age of 50.
- Diet: Eating foods that are high in fat and low in fiber may increase the risk of colorectal cancer.
- Physical inactivity: A sedentary lifestyle and not enough physical activity has been reported to be associated with a higher risk of colorectal cancer.
The earliest sign of colon cancer may be bleeding. Most of the tumors bleed only small amounts and the bleeding is occasional. Evidence of the blood is found during chemical testing of the feces for hidden (occult) blood. This is called fecal occult blood test. When tumors grow to a large size, they may cause a change in the bowel habits. The stools may be very narrow in diameter. There may be other symptoms of general stomach discomfort, such as a feeling of fullness or bloating, stomach cramps, gas pains, diarrhea or constipation.Sometimes the patient complains of a feeling that the bowel does not empty completely. Constant tiredness and weight loss with no known reason may be other warning signs. Many of these symptoms can be caused by conditions other than cancer, however they must be evaluated by a doctor without delay.
If the doctor suspects colon cancer, then he or she may use one of the following tests to find out if the disease is present. A thorough physical examination will be conducted to check all symptoms and a complete medical history will be taken to assess any risk factors. A digital rectal examination will bedone during the physical. In this procedure, the physician inserts a gloved finger into the rectum to feel for anything abnormal. This simple test can help to detect many rectal cancers. A fecal occult blood test may be ordered, where a sample of stool is examined for blood.
A sigmoidoscopy may be done to enable the doctor to look inside the rectum and part of the colon. A colonoscopy will be ordered if the doctor wishes to examine the entire colon lining. If a suspicious mass is detected, then the doctor may cut out a small piece to examine it under a microscope and see if there are any cancer cells. This procedure is called a biopsy.
Another test that is used to diagnose colon cancer is known as a double contrast barium enema. The patient is given a barium sulfate enema through the anus. This is a chalky substance that partially fills and opens the colon. Whenthe colon is about half full of barium, the patient is turned on the x-ray table so that the barium spreads throughout the colon. Air is then inserted into the colon to make it expand and x-ray films are taken.
Treatment for colon and rectal cancers depend on the stage of the cancer (theextent to which it has spread). The standard modes of treatment are surgery,radiation therapy and chemotherapy.
Surgery is the main treatment for colon cancer. If the cancer is found at a very early stage, the doctor may take out the cancer without cutting into theabdomen. Instead the doctor may put a tube through the rectum into the colonand cut the tumor out. If the cancer is larger but confined to a portion of the colon, the abdomen is opened up and the cancerous growth and a small pieceof normal tissue from either side of the cancer is removed. If there is anylikelihood of the cancer having spread to the nearby lymphnodes, they may beremoved as well. The remaining sections of the colon are then attached back together.
If the doctor is not able to sew the colon back together, he will make an opening called the stoma on the outside of the body for the waste material to pass out of the body. This is called a colostomy. Sometimes the colostomy is temporary until the colon is healed and then it can be reversed. However, if the surgery involves taking out the entire lower colon, a permanent colostomy is needed.
In the case of rectal cancer, different surgical methods are used. When the cancer is found in the polyps, a procedure known as polypectomy is used. Localexcision is used to remove small superficial cancers. If the cancer is in the deeper layers of the rectum, a cut is made through all the layers of the rectum to remove the invasive cancer as well as some surrounding normal rectaltissue. All of these methods can be done without cutting through the abdomen.
Radiation therapy involves the use of high-energy radiation to kill cancer cells. It can be applied to both colon and rectal cancers. Radiation therapy isgenerally used after the surgery to destroy any cancerous material that maynot have been removed during surgery. If the tumor is in a place that makes surgery hard, then radiation may be used before surgery to shrink the tumor. In advanced cancers, where surgery is not an option, radiation may be used toease the symptoms such as pain, blockage or bleeding.
In colorectal cancers, chemotherapy is generally used after surgery to destroy any cancerous cells that may have migrated from the original site and spread to other parts. The anti-cancer drugs are either given through a vein in the arm or by mouth, in the form of pills. In the case of advanced cancers, chemotherapy may be given to alleviate symptoms.
The death rate from colorectal cancer has been going down for the past 20 years. This may be because of the advanced methods of early detection and improved treatment modes. If colorectal cancer is detected at an early stage and iftreated appropriately, 92% of the people will survive 5 years or more. If the disease has spread to distant sites such as the liver or the lung, the outlook is not good, with only 7% of the patients surviving 5 years after initialdiagnosis.
Although the exact cause of colorectal cancer is not known, it is possible toprevent many colon cancers by avoiding the risk factors. By following the screening guidelines, the number of colon cancer cases can be lowered, and by detecting the disease at an earlier stage, the death rate can be lowered.
The American Cancer Society recommends that beginning at age 50, both men andwomen should follow the schedule for early detection of colorectal cancer. This includes a yearly fecal occult blood test, and an annual digital rectal examination. Flexible sigmoidoscopy should be done every 5 years, and a colonoscopy every 5 - 10 years. A barium enema x ray should also be done every 5 -10 years.
Proper diet and exercise go a long way in preventing colorectal cancer. The American Cancer Society recommends eating at least five servings of fruits andvegetables every day and six servings of food from plant sources such as breads, cereals, grain products, rice, pasta, or beans. Avoiding high-fat, low-fiber foods, such as red meat and processed foods, is also advised. Achievingand maintaining an ideal body weight by at least 30 minutes of physical activity every day is recommended.