Colon Cancer

What is Colon Cancer?

The colon and rectum are parts of the digestive system, which is also called the gastrointestinal, or GI, system (see picture below). The first part of digestive system processes food for energy while the last part (the colon and rectum) removes solid waste (fecal matter or stool) from the body. In order to understand colorectal cancer, it helps to have some basic knowledge about the normal structure and function of the digestive system.

The colon has 4 sections:

• The first section is called the ascending colon. It starts with a small pouch (the cecum) where the small bowel attaches to the colon and extends upward on the right side of the abdomen. The cecum is also where the appendix attaches to the colon.
• The second section is called the transverse colon since it goes across the body from the right to the left side in the upper abdomen.
• The third section, the descending colon, continues downward on the left side.
• The fourth and last section is known as the sigmoid colon because of its "S" or "sigmoid" shape.

Colorectal cancer is a term that is used to refer to cancer that develops in the colon or the rectum. These cancers are sometimes referred to separately as colon cancer or rectal cancer, depending on where they start.

The wall of the colon and rectum is made up of several layers of tissue. Colorectal cancer starts in the innermost layer and can grow through some or all of the other layers.

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Why is colon cancer a concern for American Indians?

Colon and Rectum Cancer Incidence Rates: Alaska Natives living in the state of Alaska have the highest age-adjusted colon and rectum cancer incidence rate per 100,000 population for both sexes (Alaska, 1977-83) in comparison with all other racial groups, such as blacks and whites. The Alaska Natives rate is 62.6/100,000 and the white rate is 52.8/100,000. The American Indian both sexes colon and rectum cancer incidence rate is significantly lower among American Indians living in Arizona and New Mexico, with a rate of 10.2 per 100,000. When tribal and IHS Area data are reviewed, the most striking data are for Alaska Natives. Alaska Native males have a colon and rectum cancer incidence rate of 61.0 which is similar to the white male rate of 64.5. Aleut males have a colon and rectum cancer incidence rate of 114.8. Other Alaska Native male groups are significantly lower in colon and rectum incidence rates. Eskimo males have a rate of 53.2 and Athapaskan Alaska Native males have a rate of 40.4.
The American Indian male colorectal incidence rate from Arizona and New Mexico is the lowest of any racial group at 10.6. Alaska Native female colon and rectum incidence rate is the highest of any racial group with a rate of 65.2 (the second highest rate is 45.9 for black women). Aleut females also have a high rate (89.9), but in comparison to the other Alaska Native groups, their rate is the lowest. Eskimo Alaska Native women have the highest rate of any other Alaska Native group at 116.1 and Athapaskan women have a rate of 96.2.
The white female rate in comparison is 44.9 and the American Indian female rate from Arizona and New Mexico is exceptionally low at 10.0.
Among American Indians, the Bemidji Area is the only area which has elevated rates. The Bemidji male rate of 58.0 is very similar to the SEER white rate. The Bemidji female rate of 57.7 is a higher incidence that white women.

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What causes colon cancer?

Although there is no known exact cause of most colorectal cancers, there is a great deal of research in this area. Researchers are beginning to understand how certain changes in DNA (DNA mutations) can cause normal cells to become cancerous.

DNA mutations may be passed on from generation to generation. When this happens, the mutations are inherited. Other mutations happen during an individual's lifetime and are not passed on. These DNA changes are called acquired mutations. These are the most common type of mutations. Some of the same genes are involved in both hereditary and acquired mutations.

A small percentage of colorectal cancers are known to be caused by inherited gene mutations. Many of these DNA changes and how they can change the growth control of cells are now known.

• Inherited changes in a gene called APC, for example, are responsible for familial adenomatous polyposis (FAP) and Gardner syndrome. The APC gene is a tumor suppressor gene -- it normally helps keep cell growth in check. Over time, cancer will nearly always develop in one or more of these polyps because new gene mutations occur in the cells of the polyps.
• Hereditary nonpolyposis colon cancer (HNPCC), also know as Lynch syndrome, is caused by changes in genes that normally help a cell repair faulty DNA. Cells must make a new copy of their DNA each time they divide. Sometimes errors are made when copying the DNA code. These errors will sometimes affect growth-regulating genes, which may lead to the development of cancer.

In most cases of colorectal cancer, the DNA mutations that lead to cancer are acquired during a person's life rather than having been inherited. While certain risk factors likely play a role in causing these acquired mutations, so far the cause of most of these mutations remains unknown. There does not seem to be a single pathway to colorectal cancer that is the same in all cases.

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What are some of the various types of colon cancer?

Before a cancer develops, a growth of tissue or tumor usually begins as a non-cancerous polyp on the inner lining of the colon or rectum. A tumor is abnormal tissue and can be benign (not cancer) or malignant (cancer). A polyp is a benign, non-cancerous tumor. Some polyps can change into cancer but not all do. The chance of changing into a cancer depends upon the kind of polyp:

• Adenomatous polyps (adenomas) are polyps that have the potential to change into cancer. Because of this, adenomas are called a pre-cancerous condition.
• Hyperplastic polyps and inflammatory polyps, in general, are not pre-cancerous. But some doctors think that some hyperplastic polyps can become pre-cancerous or might be a sign of having a greater risk of developing adenomas and cancer, particularly when these polyps grow in the ascending colon.

Another kind of pre-cancerous condition is called dysplasia. Dysplasia is an area in the lining of the colon or rectum where the cells look abnormal (but not like true cancer cells) when viewed under a microscope. These cells have the potential to change into cancer over time. This is usually seen in people who have had diseases such as ulcerative colitis or Crohns disease for many years. Both ulcerative colitis and Crohns disease cause chronic inflammation of the colon.

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What are the risk factors of colon cancer?

Researchers have found several risk factors that may increase a person's chance of developing colorectal polyps or colorectal cancer. Such risk factors include:

• Age- While younger adults can develop colorectal cancer, the chances of developing colorectal cancer increase markedly after age 50. More than 90% of people diagnosed with colorectal cancer are older than 50.
• Personal history of colorectal polyps or colorectal cancer- If you have a history of adenomatous polyps (adenomas), you are at increased risk of developing colorectal cancer. This is especially true if the polyps are large or if there are many of them. If you have had colorectal cancer, even though it has been completely removed, you are more likely to develop new cancers in other areas of the colon and rectum. The chances of this happening are greater if you had your first colorectal cancer when you were younger than age 60.
• Personal history of inflammatory bowel disease-  Inflammatory bowel disease (IBD), which includes ulcerative colitis and Crohn's disease, is a condition in which the colon is inflamed over a long period of time. If you have IBD, your risk of developing colorectal cancer is increased, and you need to be screened for colorectal cancer on a more frequent basis. Often the first sign that cancer may be developing is called dysplasia. Dysplasia is a term that refers to abnormal cells that have the potential to progress to cancer. Inflammatory bowel disease is different than irritable bowel syndrome (IBS), which does not carry an increased risk for colorectal cancer.
• Family history of colorectal cancer- Most colorectal cancers occur in people without a family history of colorectal cancer. Still, up to 20% of people who develop colorectal cancer have other family members who have been affected by this disease. People with a history of colorectal cancer or adenomatous polyps in one or more first-degree relatives (parents, siblings, children) are at increased risk. The risk is about doubled in those with a single affected first-degree relative, and is even higher in people with a stronger family history, such as:
  • a history of colorectal cancer or adenomatous polyps in any first-degree relative (parent, sibling, or child) younger than age 60
  • a history of colorectal cancer or adenomatous polyps in 2 or more first-degree relatives at any age

The reasons for the increased risk are not clear in all cases. Cancers can "run in the family" because of inherited genes, shared environmental factors, or some combination of these. People diagnosed with adenomatous polyps or colorectal cancer should inform other family members. Those with a family history of colorectal cancer need to talk with their doctor about the possible need to begin screening before age 50.

• Inherited syndromes- About 5% of people who develop colorectal cancer have an inherited genetic susceptibility to the disease. The 2 most common inherited syndromes linked with colorectal cancers are familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC).
• Familial adenomatous polyposis (FAP)- FAP is caused by changes (mutations) in the APC gene that a person inherits from his or her parents. About 1% of all colorectal cancers are due to FAP. People with this disease typically develop hundreds or thousands of polyps in their colon and rectum, usually in their teens or early adulthood. Cancer usually develops in 1 or more of these polyps as early as age 20. By age 40, almost all people with this disorder will have developed cancer if preventive surgery (removing the colon) is not done. FAP is sometimes associated with Gardner syndrome, a condition that involves benign (non-cancerous) tumors of the skin, soft connective tissue, and bones.
• Hereditary non-polyposis colon cancer (HNPCC)- HNPCC, also known as Lynch syndrome, is another clearly defined genetic syndrome. It accounts for about 3% to 4% of all colorectal cancers. HNPCC can be caused by inherited changes in a number of different genes that normally help repair DNA damage. This syndrome also develops when people are relatively young. People with HNPCC have polyps, but they only have a few, not hundreds as in FAP. The lifetime risk of colorectal cancer in people with this condition may be as high as 70% to 80%. Women with this condition also have a very high risk of developing cancer of the endometrium (lining of the uterus). Other cancers linked with HNPCC include cancer of the ovary, stomach, small bowel, pancreas, kidney, ureters (tubes that carry urine from the kidneys to the bladder), and bile duct.
• Peutz-Jeghers syndrome- People with this rare inherited condition tend to have freckles around the mouth (and sometimes on the hands and feet) and large polyps in their digestive tracts. They are at greatly increased risk for colorectal cancer, as well as several other cancers, which usually appear at a younger than normal age. Identifying families with these inherited syndromes is important because it allows doctors to recommend specific steps, such as screening and other preventive measures, at an early age. Because several types of cancer can be linked with these syndromes, people should check their family medical history for polyps or any type of cancer. Those who develop polyps or cancer should inform other family members. People with a family history of colorectal polyps or cancer should consider genetic counseling to review their family medical tree and determine whether genetic testing may be right for them. If needed, this can help them to decide about getting screened and treated at an early age.
• Racial and ethnic background- African Americans have the highest colorectal cancer incidence and mortality rates of all racial groups in the United States. The reason for this is not yet understood. Jews of Eastern European descent (Ashkenazi Jews) have one of the highest colorectal cancer risks of any ethnic group in the world. Several gene mutations leading to an increased risk of colorectal cancer have been found in this group. The most common of these DNA changes, called the I1307K APC mutation, is present in about 6% of American Jews.
• Lifestyle-related factors- Several lifestyle-related factors have been linked to colorectal cancer. In fact, the links between diet, weight, and exercise and colorectal cancer risk are some of the strongest for any type of cancer.
• Certain types of diets- A diet that is high in red meats (beef, lamb, or liver) and processed meats (hot dogs, bologna, and luncheon meat) can increase colorectal cancer risk. Methods of cooking meats at very high temperatures (frying, broiling, or grilling) create chemicals that might increase cancer risk, although it's not clear how much this might contribute to an increase in colorectal cancer risk. Diets high in vegetables and fruits have been linked with a decreased risk of colorectal cancer. Whether other dietary components (fiber, certain types of fats, etc.) affect colorectal cancer risk is not clear.
• Physical inactivity- If you are not physically active, you have a greater chance of developing colorectal cancer. Increasing activity may help reduce your risk.
• Obesity- If you are very overweight, your risk of developing and dying from colorectal cancer is increased. While obesity raises the risk of colon cancer in both men and women, the link seems to be stronger in men.
• Smoking- Long-term smokers are more likely than non-smokers to develop and die from colorectal cancer. While smoking is a well-known cause of lung cancer, some of the cancer-causing substances are swallowed and can cause digestive system cancers, such as colorectal cancer.
• Heavy alcohol use- Colorectal cancer has been linked to the heavy use of alcohol. At least some of this may be due to the fact that heavy alcohol users tend to have low levels of folic acid in the body. Still, alcohol use should be limited to no more than 2 drinks a day for men and 1 drink a day for women.
• Type 2 diabetes- People with type 2 (usually non-insulin dependent) diabetes have an increased risk of developing colorectal cancer. Both type 2 diabetes and colorectal cancer share some of the same risk factors (such as excess weight). But even after taking these into account, people with type 2 diabetes still have an increased risk. They also tend to have a less favorable prognosis (outlook) after diagnosis.

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What can you do to prevent getting colon cancer?

Regular colorectal cancer screening or testing is one of the most powerful weapons in preventing colorectal cancer. From the time the first abnormal cells start to grow, it usually takes about 10 to 15 years for them to develop into colorectal cancer. Regular colorectal cancer screening can, in many cases, prevent colorectal cancer altogether. This is because some polyps, or growths, can be found and removed before they have the chance to turn into cancer. Screening can also result in finding colorectal cancer early, when it is highly curable.
People who have no identified risk factors (other than age) should begin regular screening at age 50. Those who have a family history or other risk factors for colorectal polyps or cancer, such as inflammatory bowel disease, should talk with their doctor about starting screening at a younger age and/or getting screened at more frequent intervals.

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What are the signs / symptoms of colon cancer?

Many people with colon cancer experience no symptoms in the early stages of the disease. When symptoms appear, they'll likely vary, depending on the cancer's size and location in your large intestine.
Signs and symptoms of colorectal cancer
If you have any of the following you should check with your doctor for prompt diagnosis and treatment:

• a change in bowel habits, such as diarrhea, constipation, or narrowing of the stool, that lasts for more than a few days 
• a feeling that you need to have a bowel movement that is not relieved by doing so
• rectal bleeding, dark stools, or blood in the stool (often, though, the stool will look normal) 
• cramping or abdominal (stomach area) pain 
• weakness and fatigue
• weight loss

Most of these symptoms are more likely to be caused by conditions other than colorectal cancer, such as infection, hemorrhoids, or inflammatory bowel disease. Blood in your stool may be a sign of cancer, but it can also indicate other conditions. Bright red blood you notice on bathroom tissue more commonly comes from hemorrhoids or minor tears (fissures) in your anus, for example. In addition, certain foods, such as beets or red licorice, can turn your stools red. Iron supplements and some anti-diarrheal medications may make stools black. Still, it's best to have any sign of blood or change in your stools checked promptly by your doctor because it can be a sign of something more serious.

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How is colon cancer detected?

Colon cancer is detected through screening. Screening is the process of looking for cancer in people who have no symptoms of the disease. There are several different tests that can be used to screen for colorectal cancers.

These tests can be divided into 2 broad groups:

• Tests that can find both colorectal polyps and cancer: These tests look at the structure of the colon itself to find any abnormal areas. This is done either with a scope inserted into the rectum or with special imaging (x-ray) tests. Polyps found before they turn cancerous can be removed, so these tests may prevent colorectal cancer. Because of this, they are preferred if they are available and you are willing to have them.
• Tests that mainly find cancer: These involve testing the stool (feces) for signs that cancer may be present. These tests are less invasive and easier to have done, but they are less likely to detect polyps. These tests as well as others can also be used when people have symptoms of colorectal cancer and other digestive diseases.

Other Colorectal cancer screening tests include:

Flexible sigmoidoscopy- During this test, the doctor looks at part of the colon and rectum with a sigmoidoscope -- a flexible, lighted tube about the thickness of a finger with a small video camera on the end. It is inserted through the rectum and into the lower part of the colon. Images from the scope are viewed on a display monitor. Using the sigmoidoscope, your doctor can view the inside of the rectum and part of the colon to detect (and possibly remove) any abnormality. Because the sigmoidoscope is only 60 centimeters (about 2 feet) long, the doctor is able to see the entire rectum but less than half of the colon with this procedure.

Colonoscopy- For this test, the doctor looks at the entire length of the colon and rectum with a colonoscope, which is basically a longer version of a sigmoidoscope. It is inserted through the rectum into the colon. The colonoscope has a video camera on the end that is connected to a display monitor so the doctor can see and closely examine the inside of the colon. Special instruments can be passed through the colonoscope to remove any suspicious looking areas such as polyps, if needed.
Colonoscopy may be done in a hospital outpatient department, in a clinic, or in a doctor's office.

Double contrast barium enema (DCBE)- This procedure is also called an air-contrast barium enema or a barium enema with air contrast. It is basically a type of x-ray test. Barium sulfate, which is a chalky liquid, and air are used to outline the inner part of the colon and rectum to look for abnormal areas on x-rays. If suspicious areas are seen on this test, a colonoscopy will be needed to explore them further.

CT colonography (virtual colonoscopy)- This test is an advanced type of computed tomography (CT or CAT) scan of the colon and rectum. A CT scan is an x-ray test that produces detailed cross-sectional images of your body. Instead of taking one picture, like a regular x-ray, a CT scanner takes many pictures as it rotates around you while you lie on a table. A computer then combines these pictures into images of slices of the part of your body being studied. CT colonography involves the use of special computer programs to create both two dimensional x-ray pictures and a three-dimensional "fly-through" view of the inside of the colon and rectum, which allows the doctor to look for polyps or cancer.

Fecal occult blood test- The fecal occult blood test (FOBT) is used to find occult (hidden) blood in feces. The idea behind this test is that blood vessels at the surface of larger colorectal polyps or cancers are often fragile and easily damaged by the passage of feces. The damaged vessels usually release a small amount of blood into the feces, but only rarely is there enough bleeding to be noticeable in the stool.
The FOBT detects blood in the stool through a chemical reaction. This test cannot tell whether the blood is from the colon or from other portions of the digestive tract (such as the stomach). Therefore, if this test is positive, a colonoscopy is needed to see if there is a cancer, polyp, or other cause of bleeding such as ulcers, hemorrhoids, diverticulosis (tiny pouches that form at weak spots in the colon wall), or inflammatory bowel disease (colitis).
If this test finds blood, a colonoscopy will be needed to look for the source. It is not sufficient to simply repeat the FOBT or follow up with other types of tests.

Fecal immunochemical test- The fecal immunochemical test (FIT), also called an immunochemical fecal occult blood test (iFOBT), is a newer kind of test that also detects occult (hidden) blood in the stool. This test reacts to part of the hemoglobin molecule, which is found on red blood cells.
The FIT is done essentially the same way as the FOBT, but some people may find it easier to use because there are no drug or dietary restrictions (vitamins or foods do not affect the FIT) and sample collection may take less effort. This test is also less likely to react to bleeding from the upper digestive tract, such as the stomach.
As with the FOBT, the FIT may not detect a tumor that is not bleeding, so multiple stool samples should be tested. And if the results are positive for hidden blood, a colonoscopy is required to investigate further. In order to be beneficial the test must be repeated every year.

Stool DNA tests- Theses tests look for certain abnormal sections of DNA (genetic material) from cancer or polyp cells. Colorectal cancer cells often contain DNA mutations (changes) in certain genes such as APC, K-ras, and p53. Cells from colorectal cancers or polyps with these mutations are often shed into the stool, where tests may be able to detect them.

• This is a newer test, and the best length of time to go between tests is not yet clear. This test is also much more expensive than other forms of stool testing.
• This test is not invasive and doesn't require any special preparation. But as with other stool tests, if the results are positive, a colonoscopy is required to investigate further.
• People having this test will receive a kit with detailed instructions from their doctor's office or clinic on how to collect the specimen. Always follow the instructions on your kit.
• This test requires an entire stool sample. It is obtained using a special container, which is placed in a bracket that stretches across the seat of the toilet. You have your bowel movement while sitting on the toilet, making sure it goes into the container. You then place the container and an ice pack in a shipping box and close and label the box. The specimen must be shipped to the lab within 24 hours of having the bowel movement.

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What treatments are available for colon cancer?

The main types of treatment for colon cancer and rectal cancer are:

• surgery 
• radiation therapy 
• chemotherapy 
• targeted therapies

Depending on the stage of the cancer, 2 or more of these types of treatment may be combined at the same time or used after one another.

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