Colon cancer metastasis

Definition

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 form tumors.

Description

Colorectal cancer is the third most common cancer, behind lung and prostate cancer in men, and breast and lung cancer in women. The American Cancer Society (ACS) estimates that colorectal cancers will account for about 11% of all new cancer cases in 1998. They will result in about 10% of all cancer deaths. The incidence of colorectal cancer is divided equally among both men and women, with the risk usually beginning after 40 years of age. The average age at first diagnosis is 60-65 years.

The main function of the colon is to absorb water and the nutrients from the food 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 moves upward to the hepatic flexure. It then becomes the transverse colon moving across to the liver. When reaching the spleen, the colon continues as the descending colon and moves down to the pelvis area. It is then called the sigmoid colon and extends to the 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 have different 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 the intestine. These benign growths are called polyps. Most of the polyps are not cancerous. Nevertheless, virtually all colorectal cancers begin from these benign growths. 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, have the potential to become cancerous.

Causes & symptoms

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, even when polyps are not present) are present in certain families and 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 are harmless, some particular types do increase the risk of colorectal cancer, especially if they are large and there are many of them.
• Inflammatory bowel disease: Chronic ulcerative colitis, a condition in which the colon is inflamed over a long period of time and causes ulcers in the lining, can increase the risk of colon cancer.
• Age: About 90% of colorectal cancers are 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.

Diagnosis

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 be done 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. The test kit can be purchased at any local pharmacy. The test involves taking a sample of stool and smearing it on a slide. This is then sent to the laboratory or to the doctors' office where it will be chemically examined for the presence of red blood cells.

A sigmoidoscopy may be done to enable the doctor to look inside the rectum and part of the colon. In this procedure, a thin flexible hollow lighted tube (sigmoidoscope) is placed into the rectum. The doctor then looks inside the scope for small growths called polyps. Since they may become cancerous, they should be removed.

A colonoscopy will be ordered if the doctor wishes to examine the entire colon lining. A colonoscope is longer than a sigmoidoscope and is inserted through the rectum into the colon. It is connected to a video camera and a video display unit so that the doctor can look at the inside of the colon. 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. When the 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

Treatment for colon and rectal cancers depend on the stage of the cancer (the extent to which it has spread). The standard modes of treatment are surgery, radiation therapy and chemotherapy.