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Health Library : Digestive Disorders

 

Colorectal Cancer

Anatomy of the Colon

The colon is the large intestine. It 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.

What is colorectal cancer?

Colorectal cancer is malignant cells found in the colon or rectum. The colon and the rectum are parts of the large intestine, which is part of the digestive system. Because colon cancer and rectal cancers have many features in common, they are sometimes referred to together as colorectal cancer. Cancerous tumors found in the colon or rectum also may spread to other parts of the body.

Excluding skin cancers, colorectal cancer is the third most common cancer in both men and women. The American Cancer Society estimates that about 140,000 colorectal cancer cases and about 50,000 deaths from colorectal cancer occur each year. The number of deaths due to colorectal cancer has decreased, which is attributed to increased screening and polyp removal and to improvements in cancer treatment.

What are the types of cancer in the colon and rectum?

A type of cancer called adenocarcinoma accounts for more than 95 percent of cancers in the colon and rectum, and is usually what is meant by the term "colorectal cancer." It is the type we focus on in this section. There are other types of cancer that can be found in the colon and rectum, but they are rare.

Here is an overview of the types of cancer in the colon and rectum:

  • adenocarcinoma
    Adenocarcinomas are tumors that start in the lining of internal organs. "Adeno" means gland. These tumors start in cells with glandular properties, or cells that secrete. They can form in many different organs, such as the lung or the breast. In colorectal cancer, early tumors start as small adenomatous polyps that continue to grow and can then turn into malignant tumors. The vast majority of colorectal cancers are adenocarcinomas.
  • gastrointestinal stromal tumors (GIST)
    These are tumors that start in specialized cells in the wall of the digestive tract called the interstitial cells of Cajal. These tumors may be found anywhere in the digestive tract, although they rarely appear in the colon. They can be benign (noncancerous) at first, but many do turn into cancer. When this happens, they are called sarcomas. Surgery is the usual treatment if the tumor has not spread.
  • lymphoma
    A lymphoma is a cancer that typically starts in a lymph node, which is part of the immune system. However, it can also start in the colon, rectum, or other organs.
  • carcinoids
    Carcinoids are tumors that start in special hormone-producing cells in the intestine. Often they cause no symptoms at first. Surgery is the usual treatment.
  • sarcoma
    Tumors that start in blood vessels as well as in muscle and connective tissue in the wall of the colon and rectum.

What are the symptoms of colorectal cancer?

The following are the most common symptoms of colorectal cancer. However, each individual may experience symptoms differently.

People who have any of the following symptoms should check with their physicians, especially if they are over 50 years old or have a personal or family history of the disease:

  • a change in bowel habits such as diarrhea, constipation, or narrowing of the stool that lasts for more than a few days
  • rectal bleeding or blood in the stool
  • cramping or gnawing stomach pain
  • decreased appetite
  • vomiting
  • unintended weight loss
  • weakness and fatigue
  • a feeling that you need to have a bowel movement that is not relieved by doing so

The symptoms of colorectal cancer may resemble other conditions, such as infections, hemorrhoids, and inflammatory bowel disease. It is also possible to have colon cancer and not have any symptoms. Always consult your health care provider for a diagnosis.

What are the risk factors for colorectal cancer?

Risk factors may include:

What is a Risk Factor?

A risk factor is anything that may increase a person's chance of developing a disease. It may be an activity, such as smoking, diet, family history, or many other things. Different diseases, including cancers, have different risk factors.

Although these factors can increase a person's risk, they do not necessarily cause the disease. Some people with one or more risk factors never develop the disease, while others develop disease and have no known risk factors. But, knowing your risk factors to any disease can help to guide you into the appropriate actions, including changing behaviors and being clinically monitored for the disease.

  • age
    Most people who have colorectal cancer are over age 50; however, it can occur at any age.
  • race and ethnicity
    African Americans have the highest risk for colorectal cancer of all racial groups in the U.S. Jews of Eastern European descent (Ashkenazi Jews) have the highest colorectal cancer risk of any ethnic group in the world.
  • diet
    Colorectal cancer is often associated with a diet high in red and processed meats.
  • personal history of colorectal polyps
    Benign growths on the wall of the colon or rectum are common in people over age 50, and may lead to colorectal cancer.
  • personal history of colorectal cancer
    People who have had colorectal cancer have an increased risk for another colorectal cancer.
  • family history
    People with a strong family history of colorectal cancer or polyps in a first-degree relative (especially in a parent or sibling before the age of 45 or in two first-degree relatives of any age), have an increased risk for colorectal cancer.
  • ulcerative colitis or Crohn's disease
    People who have an inflamed lining of the colon have an increased risk for colorectal cancer.
  • inherited syndromes such as familial adenomatous polyposis (FAP) or hereditary nonpolyposis colon cancer (HNPCC), also known as Lynch syndrome
  • obesity
  • physical inactivity
  • heavy alcohol consumption
  • type 2 diabetes
  • smoking

What causes colorectal cancer?

The exact cause of most colorectal cancer is unknown, but the known risk factors listed above are the most likely causes. A small percentage of colorectal cancers are caused by inherited gene mutations. People with a family history of colorectal cancer may wish to consider genetic testing. The American Cancer Society suggests that anyone undergoing such tests have access to a physician or geneticist qualified to explain the significance of these test results.

Prevention of colorectal cancer:

Although the exact cause of colorectal cancer is not known, it is possible to prevent many colon cancers with the following:

  • diet, weight and exercise
    It is important to manage the risk factors you can control, such as diet, body weight, and exercise. Eating more fruits, vegetables, and whole grain foods, and limiting red and processed meats, plus exercising appropriately, even small amounts on a regular basis, can be helpful.
  • drug therapy
    Some studies have shown that low doses of nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, and hormone replacement therapy for post-menopausal women may reduce the risk of colorectal cancer. But these drugs also have their own potentially serious risks, so it is important to discuss this with your health care provider.
  • screenings
    Perhaps most important to the prevention of colorectal cancer is having screening tests at appropriate ages. Screenings may find some colorectal polyps that can be removed before they have a chance to become cancerous. Because some colorectal cancers cannot be prevented, finding them early is the best way to improve the chance of successful treatment, and reduce the number of deaths caused by colorectal cancer.

    The following screening guidelines can lower the number of cases of the disease, and can also lower the death rate from colorectal cancer by detecting the disease at an earlier, more treatable stage.

Methods of screening for colorectal cancer:

Screening methods for colorectal cancer, for people who do not have any symptoms or strong risk factors, include the following:

  • fecal occult blood test (FOBT) - checks for hidden (occult) blood in the stool. It involves placing a very small amount of stool on a special card, which is then tested in the physician's office or sent to a laboratory.
  • fecal immunochemical test (FIT) - a test that is similar to a fecal occult blood test, but does not require any restrictions on diet or medications prior to the test.
  • flexible sigmoidoscopy - a diagnostic procedure that allows the physician to examine the inside of a portion of the large intestine, and is helpful in identifying the causes of diarrhea, abdominal pain, constipation, abnormal growths, and bleeding. A short, flexible, lighted tube with a small video camera on the end, called a sigmoidoscope, is inserted into the intestine through the rectum. The scope blows air into the intestine to inflate it and make viewing the inside easier.
  • colonoscopy - a procedure that allows the physician to view the entire length of the large intestine, and can often help identify abnormal growths, inflamed tissue, ulcers, and bleeding. It involves inserting a colonoscope, a long, flexible, lighted tube, in through the rectum up into the colon. The colonoscope allows the physician to see the lining of the colon, remove tissue for further examination, and possibly treat some problems that are discovered.
  • CT colonography (virtual colonoscopy) - a procedure that uses computerized tomography (CT) scans to examine the colon for polyps or masses. The images are processed by a computer to make a 3-dimensional (3-D) model of the colon. Virtual colonoscopy is non-invasive, although it requires a small tube to be inserted into the rectum to pump air into the colon. If something abnormal is seen with this test, a standard colonoscopy will be needed as follow up.

Illustration demonstrating a colonoscopy, part 1
Click Image to Enlarge
Illustration demonstrating a colonoscopy, part 2
  • barium enema with air contrast (Also called a double contrast barium enema.) - a fluid called barium (a metallic, chemical, chalky, liquid used to coat the inside of organs so that they will show up on an x-ray) is given into the rectum to partially fill up the colon. Air is then pumped in to expand the colon and rectum. An x-ray of the abdomen shows strictures (narrowed areas), obstructions (blockages), and other problems.
Screening Guidelines for Colorectal Cancer
Colorectal cancer screening guidelines from the American Cancer Society for early detection include:
  • Beginning at age 50, both men and women should follow one of the examination schedules below:
    • fecal occult blood test (FOBT) or fecal immunochemical test (FIT) every year
    • flexible sigmoidoscopy (FSIG) every five years
    • double-contrast barium enema every five years
    • colonoscopy every 10 years
    • CT colonography (virtual colonoscopy) every five years
  • People with any of the following colorectal cancer risk factors should begin screening procedures at an earlier age and/or be screened more often:
    • strong family history of colorectal cancer or polyps in a first-degree relative, especially in a parent or sibling before the age of 45 or in two first-degree relatives of any age
    • family with hereditary colorectal cancer syndromes, such as familial adenomatous polyposis (FAP) and hereditary nonpolyposis colon cancer (HNPCC)
    • personal history of colorectal cancer or adenomatous polyps
    • personal history of chronic inflammatory bowel disease (Crohn's disease or ulcerative colitis)

Diagnostic procedures for colorectal cancer:

If a person has symptoms that might be caused by colorectal cancer, the doctor will want to get a complete medical history and do a physical examination. The doctor may also do certain tests to look for cancer. Many of these tests are the same as those done to screen for colorectal cancer in people without symptoms.

  • digital rectal examination (DRE) - a physician or healthcare provider inserts a gloved and lubricated finger into the rectum to feel for anything unusual or abnormal. This test can detect some cancers of the rectum, but not the colon.
  • fecal occult blood test - checks for hidden (occult) blood in the stool. It involves placing a very small amount of stool on a special card, which is then tested in the physician's office or sent to a laboratory.
  • flexible sigmoidoscopy - a diagnostic procedure that allows the physician to examine the inside of a portion of the large intestine. A short, flexible, lighted tube with a small video camera on the end, called a sigmoidoscope, is inserted into the intestine through the rectum. The scope blows air into the intestine to inflate it and make viewing the inside easier.
  • colonoscopy - a procedure that allows the physician to view the entire length of the large intestine. It involves inserting a colonoscope, a long, flexible, lighted tube, in through the rectum up into the colon. The colonoscope allows the physician to see the lining of the colon, remove tissue for further examination, and possibly treat some problems that are discovered.
  • barium enema - (also called double contrast barium enema). A fluid called barium (a metallic, chemical, chalky, liquid used to coat the inside of organs so that they will show up on an x-ray) is given into the rectum to partially fill up the colon. An x-ray of the abdomen shows strictures (narrowed areas), obstructions (blockages), and other problems.
  • biopsy - a procedure in which polyps or tissue samples are removed (during a colonoscopy or surgery) from the body for examination under a microscope; to determine if cancer or other abnormal cells are present.
  • blood count - a test to check for anemia (that can be a result of bleeding from a tumor).
  • imaging tests - tests such as a CT scan, PET scan, ultrasound, or MRI of the abdomen may be done to look for tumors or other problems. These tests may also be done if colorectal cancer has already been diagnosed to help determine the extent (stage) of the cancer.

What are the stages of colorectal cancer?

When colorectal cancer is diagnosed, tests will be performed to determine how much cancer is present, and if the cancer has spread from the colon or rectum to other parts of the body. This is called staging, and is an important step toward planning a treatment program. The stages for colorectal cancer are as follows:

Stage 0 (Cancer in Situ) The cancer is found in the innermost lining of the colon or rectum.
Stage I (also called Dukes A colon cancer) The cancer has spread beyond the innermost lining of the colon or rectum to the second and third layers. The cancer has not spread to the outer wall or outside of the colon or rectum.
Stage II (also called Dukes B colon cancer) The cancer has spread through the wall or outside the colon or rectum to nearby tissue. However, the lymph nodes are not involved.
Stage III (also called Dukes C colon cancer) The cancer has spread to nearby lymph nodes, but has not spread to other organs in the body.
Stage IV (also called Dukes D colon cancer) The cancer has spread to other parts of the body, such as lungs.

Treatment for colorectal cancer:

Specific treatment for colorectal cancer will be determined by your physician based on:

  • your age, overall health, and medical history
  • extent and location of the disease
  • results of certain lab tests
  • your tolerance for specific medications, procedures, or therapies
  • expectations for the course of this disease
  • your opinion or preference

After the colorectal cancer is diagnosed and staged, your physician will recommend a treatment plan. Treatment may include:

  • colon surgery
    Often, the primary treatment for colorectal cancer is an operation in which the cancer and a length of normal tissue on either side of the cancer are removed, as well as the nearby lymph nodes.
  • external beam radiotherapy (EBRT)
    EBRT uses carefully aimed beams of X-rays to kill cancer cells. EBRT is painless and takes a few minutes to deliver. The treatment plan is developed by a doctor called a Radiation Oncologist. Special techniques such as 3D-conformal, Intensity-Modulated Radiotherapy (IMRT), and Tomotherapy are often used to minimize the dose of radiation to normal tissues to reduce side effects, while still delivering enough radiation to kill tumor cells and shrink tumors. EBRT is often used before or after surgery, in combination with chemotherapy, to reduce the likelihood of tumor recurrence. EBRT is also used to ease symptoms (palliate) such as pain, blockage, or bleeding.
  • chemotherapy
    Chemotherapy is the use of anticancer drugs to treat cancerous cells. In most cases, chemotherapy works by interfering with the cancer cell's ability to grow or reproduce. Different groups of drugs work in different ways to fight cancer cells. The oncologist will recommend a treatment plan for each individual. Studies have shown that chemotherapy after surgery may increase the survival rate for patients with some stages of colon cancer. It can also be helpful before or after surgery fro some stages of rectal cancer. Chemotherapy can also help relieve symptoms of advanced cancer.

    Newer medications called targeted therapies may be used along with chemotherapy or sometimes by themselves. For example, some newer medications target proteins that are found more often on cancer cells than on normal cells. These medications have different (and often milder) side effects than standard chemotherapy medications.

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