Colon and rectal cancer develop in the digestive tract, which is also called the gastrointestinal, or GI, tract. The digestive system processes food for energy and rids the body of solid waste matter (fecal matter or stool). Colon cancer and rectal cancer have many features in common. Sometimes they are referred to together as colorectal cancer. Over 95% of colorectal cancers are ad enocarcinomas. These are cancers of the glandular cells that line the inside of the colon and rectum. Other, less common type of tumors may also develop in the colon and rectum.
Carcinoid tumors develop from hormone-producing cells of the intestine. Gastrointestinal stromal tumors develop in the connective tissue and muscle layers in the wall of the colon and rectum. Lymphomas are cancers of immune system cells that typically develop in lymph nodes but may also start in the colon and rectum or other organs. Colorectal cancers are thought to develop slowly over a period of several years. Before a true cancer develops, there usually are precancerous changes in the lining of the colon or rectum.
These changes might be dysplasia or adenomatous polyps. A polyp is a growth of tissue into the center of the colon or rectum. Some types of polyps (hyperplastic polyps and inflammatory polyps) are not precancerous. However, having adenomatous polyps, also known as adenomas, does increase a person’s risk of developing cancer, especially if there are many polyps or they are large. In contrast to the inward growth of a polyp, a true cancer can grow inward toward the hollow part of the colon or rectum, and/or outward through the wall of these organs.
If not treated, cells from the tumor may break away and spread through the bloodstream or lymph system to other parts of the body. There, they can form “colony” tumors. This process is called metastasis. The colon has four sections. The first section is called the ascending colon. It extends upward on the right side of the abdomen. The second section is called the transverse colon since it goes across the body to the left side. There it joins the third section, the descending colon, which continues downward on the left side.
The fourth section is known as the sigmoid colon because of its S-shape. The sigmoid colon joins the rectum, which in turn joins the anus, or the opening where waste matter passes out of the body. Each of these sections of the colon and rectum has several layers of tissue. Colorectal cancers start in the innermost layer and can grow through some or all of the other layers. Knowing a little about these layers is important, because the stage (extent of spread) of a colorectal cancer depends to a great degree on which of these layers it affects.
Recurrent cancer means the cancer has come back after treatment. The disease may recur in the colon or rectum or in another part of the body. The organs and their purpose are best described in the following example of the digestive system and the functions of the intestines, colon and rectum. After food is chewed and swallowed, it travels through the esophagus to the stomach. There it is partly broken down and then sent to the small intestine, also known as the small bowel. The word “small” refers to diameter of the small intestine, which is narrower than that of the large bowel.
However, the small intestine is actually the longest segment of the digestive system — about 20 feet. The small intestine continues breaking down the food and absorbs most of the nutrients. The liver and the pancreas release bile and enzymes into the small bowel to aid in this process. The small intestine joins the large intestine or large bowel, a muscular tube about five feet long. The first part of the large bowel, called the colon continues to absorb water and mineral nutrients from the food matter and serves as a storage place for waste matter.
The waste matter left after this process goes into the rectum, the final 6 inches, or so of the large bowel. From there, it passes out of the body through the anus. What are the casual factors for this disease? Colon cancer is expected to be responsible for about 47,700 deaths (23,100 men and 24,600 women) during 2000. About 8,600 people (4,700 men and 3,900 women) will die from rectal cancer during 2000. The death rate from colorectal cancer has been going down for the past 20 years. This may be because there are fewer cases, more of the cases are found early, and treatments have improved.
The 5-year relative survival rate is 90% for people whose colorectal cancer is found and treated in an early stage, before it has spread. Nevertheless, only 37% of colorectal cancers are found at that early stage. Once the cancer has spread to nearby organs or lymph nodes, the 5-year relative survival rate goes down to 65%. For people whose colorectal cancer has spread to distant parts of the body such as the liver or lungs, the 5-year relative survival rate is 8%. The 5-year survival rate refers to the percent of patients who live at least 5 years after their cancer is diagnosed.
Many of these patients live much longer than 5 years after diagnosis, and 5-year rates are used to produce a standard way of discussing prognosis. Five-year relative survival rates exclude from the calculation patients dying of other diseases, and are considered a more accurate way to describe the prognosis for patients with a particular type and stage of cancer. Of course, 5-year rates are based on patients diagnosed and initially treated more than 5 years ago. Improvements in treatment often result in a more favorable outlook for recently diagnosed patients.
What populations are susceptible to this disease? Researchers have identified several risk factors that increase a person’s chance of developing colorectal cancer. A family history of colorectal cancer: Relatives of colorectal cancer patients are also at increased risk for developing this disease. Some of these families may have a colorectal cancer syndrome such as familial adenomatous polyposis (FAP) or hereditary nonpolyposis colorectal cancer (HNPCC). Colorectal cancer may also seem to run in some families that do not have one of these syndromes.
Accurate identification of people with these syndromes is important because their doctors will recommend specific measures to prevent cancer or find it as early as possible, when treatment is most successful. Some doctors recommend that all people with colorectal cancer have an evaluation of their family history of the disease. Familial colorectal cancer syndromes: The following conditions make it more likely that a family member could develop cancer. Familial adenomatous polyposis (FAP) is a hereditary condition that greatly increases a person’s risk of developing colorectal cancer.
People with this syndrome typically develop hundreds of polyps in the colon and rectum. Cancer nearly always develops in one or more of these polyps between the ages of 30 and 50 if preventive surgery is not done. Like FAP, Gardner’s syndrome results in polyps and colorectal cancers that develop at a young age. It can also cause benign (not cancerous) tumors of the skin, soft connective tissue, and bones. Hereditary nonpolyposis colon cancer (HNPCC) develops in people at a relatively young age without first having many polyps.
Women with this condition also have an increased risk of developing cancer of the endometrium (lining of the upper part of the uterus). Recent research has found an inherited tendency to develop colorectal cancer among some Jews of Eastern European descent. Like people with FAP, Gardner’s syndrome, and HNPCC, their increased risk is due to an inherited mutation (change in DNA). This DNA change occurs much more commonly than the three other colorectal cancer syndromes, and is present in about 6% of American Jews. Additional research is needed to determine the extent to which this change increases risk.
So far, there appears to be a relatively small increase in risk, much less than that caused by FAP, Gardner’s syndrome, or HNPCC. Approximately 20 epidemiologic studies have found that people who regularly use aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) have 40% to 50% lower risk of colorectal cancer and adenomatous polyps. There are other risk factors, such as a strong family history of colorectal cancer, which people cannot control. Even when people have a history of colorectal cancer in their family, they may be able to prevent the disease.
They should ask their doctors for information and advice about prevention and early detection. For example, people with a family history of colorectal cancer may benefit from starting screening at a younger age and having screening tests done more often than people without this risk factor. Genetic tests can help determine which members of certain families have inherited a high risk for developing colorectal cancer. Most doctors recommend that people with familial adenomatous polyposis (FAP) start colonoscopy during their teens and have their colon removed during their twenties to prevent cancer from developing.
The risk for people with hereditary nonpolyposis colon cancer (HNPCC) is not as great as for those with FAP. Ashkenazi Jews with the I1307K APC mutation have a slightly increased colorectal cancer risk, but do not develop these cancers at a very young age. Among men and women, colorectal cancer is the third most common cancer diagnosed in Americans. About 93,800 new cases of colon cancer (43,400 men and 50,400 women) and 36,400 new cases of rectal cancer (20,200 men and 16,200 women) will be diagnosed in 2000.
What is the role of diet in the prevention of this disease? A diet that consists mostly of foods that are high in fat, especially from animal sources, can increase the risk of colorectal cancer. Physical inactivity; people who do not get at least a moderate degree of physical activity have an increased risk of developing colorectal cancer. Obesity; being very overweight increases a person’s colorectal cancer risk. Having excess fat in the waist area increases this risk more than having the same amount of fat in the thighs or hips.
Researchers suggest that the excess fat changes metabolism in a way that increases growth of cells in the colon and rectum, and that fat cells in the waist area have the largest impact on metabolism. Diet suggestions would include choosing most of your foods from plant sources and limiting intake of high-fat foods such as those from animal sources. A diet with five servings of fruits and vegetables every day and six servings of other foods from plant sources such as breads, cereals, grain products, rice, pasta, or beans. Many fruits and vegetables contain substances that interfere with the process of cancer formation.
According to one estimate, deaths from cancers of the colon, prostate, pancreas, and breast may be reduced a whole 50% if everyone would adopt a diet that supports good health. Is diet used in the management of the disease? Nutrition recommendations usually stress eating lots of fruits, vegetables, and whole grain breads and cereals; including a moderate amount of meat and dairy products; and cutting back on fat, sugar, alcohol, and salt. Some studies suggest that a diet low in fat and calories and high in fiber can help prevent colorectal cancer.
Studies are looking at smoking cessation, use of dietary supplements, use of aspirin or similar medicines, decreased alcohol consumption, and increased physical activity to see if these approaches can prevent colorectal cancer. Is there a cure for this disease? No, even though the exact cause of most colorectal cancer is not known, it is possible to prevent many colon cancers. Following screening guidelines can lower the number of cases of the disease by detecting and removing polyps that could become cancerous, and can also lower the death rate from colorectal cancer by finding disease early when it is highly curable.
Prevention and early detection are possible because most colon cancers develop from adenomatous polyps. Polyps are precancerous growths in the colon and rectum. Removing them can lower a person’s risk by preventing some colorectal cancers before they are fully formed. Is diet a part of this cure? People can lower their risk of developing colorectal cancer by managing the risk factors that they can control, such as diet and physical activity. It is important to eat plenty of fruits, vegetables, and whole grain foods and to limit intake of high-fat foods.
Physical activity is another area that people can control. Even small amounts of exercise on a regular basis can be helpful, at least 30 minutes of physical activity on most days. Also, achieving and maintaining a healthy weight. Some studies suggest that taking a daily multivitamin containing folic acid or folate can lower colorectal cancer risk. Other studies suggest that increasing calcium intake via supplements or low-fat dairy products may lower risk. Studies of vitamin A, C, D, and E supplements have yielded conflicting results, and additional research is needed.
