Colorectal Cancer

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. It is estimated by the American Cancer Society that about 141,000 colorectal cancer cases are expected in 2011. The number of deaths due to colorectal cancer has decreased, which is attributed to increased screening and polyp removal.

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 the muscle tissue of 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 or rectum.

• Carcinoids Carcinoids are tumors that start in special hormone-producing cells in the intestine. Often they cause no symptoms. Surgery is the usual treatment.

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 doctors, 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, dark stools, or blood in the stool

• Cramping or gnawing stomach pain

• Decreased appetite

• Vomiting

• Weight loss

• Weakness and fatigue

• Jaundice, or a yellowing of the skin and eyes

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 doctor for a diagnosis.

What are the risk factors for colorectal cancer?

Risk factors may include:

• Age Most people who have colorectal cancer are over age 50, however, it can occur at any age.

• Race African-Americans have the highest risk for colorectal cancer.

• Diet Colorectal cancer is often associated with a diet high in red and processed meats.

• Polyps Benign growths on the wall of the colon or rectum are common in people over age 50, and are believed to lead to colorectal cancer.

• Personal history People who have had colorectal cancer or a history of adenomatous polyps have an increased risk for 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 60 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)

• 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 doctor 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 may be possible to lower your risk of colorectal cancer 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 avoiding high-fat, low-fiber foods, plus exercising appropriately, even small amounts on a regular basis, can be helpful. Avoiding excess alcohol intake may also lower your risk. 

• 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. These drugs also have their own risks, so it is important to discuss this with your doctor.

• Screenings Perhaps most important to the prevention of colorectal cancer is having screening tests at appropriate ages. Screening 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. Checks for hidden (occult) blood in the stool. It involves placing a very small amount of stool on a special card, which is then 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 doctor to examine the inside of a portion of the large intestine. A short, flexible, lighted tube 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 doctor 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 doctor 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) to examine the colon for polyps or masses using special technology. The images are processed by a computer to make a 3-dimensional (3-D) model of the colon. Virtual colonoscopy is noninvasive, 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. 

• Stool DNA (sDNA). A test used to check the stool or fecal matter for specific changes in DNA (the genetic blueprint of each cell) that indicate signs of colorectal cancer. The patient is required to save an entire bowel movement and the sample is sent to a laboratory.

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• 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 administered into the rectum to partially fill up the colon. An X-ray of the abdomen is then taken and can show strictures (narrowed areas), obstructions (blockages), and other problems.

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 doctor or health care provider inserts a gloved and lubricated finger into the rectum to feel for anything unusual or abnormal. This test can detect 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 sent to a laboratory.

• Flexible sigmoidoscopy. A diagnostic procedure that allows the doctor to examine the inside of a portion of the large intestine. A short, flexible, lighted tube 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 doctor 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 doctor to see the lining of the colon, remove tissue for further examination, and possibly treat some problems that are discovered.

• 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 administered into the rectum to partially fill up the colon. An X-ray of the abdomen is then taken that can show strictures (narrowed areas), obstructions (blockages), and other problems.

• Biopsy. a procedure in which 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 (a result of bleeding from a tumor).

• Imaging tests. Tests such as a CT 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 to other parts of the body. This is called staging, and it is an important step toward planning a treatment program. The National Cancer Institute defines the following stages for colorectal cancer:

Treatment for colorectal cancer

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

• Your age, overall health, and medical history

• Extent of the disease

• 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 doctor will recommend a treatment plan. Treatment may include:

• Colon surgery Often, the primary treatment for colorectal cancer is an operation called a colon resection, 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.

• Radiation therapy Radiation therapy is the use of high-energy radiation to kill cancer cells and to shrink tumors. There are two ways to deliver radiation therapy, including the following:

  • External radiation (external beam therapy). A treatment that precisely sends high levels of radiation directly to the cancer cells. The machine is controlled by the radiation therapist. Since radiation is used to kill cancer cells and to shrink tumors, special shields may be used to protect the tissue surrounding the treatment area. Radiation treatments are painless and usually last a few minutes.

  • Internal radiation (brachytherapy, implant radiation). Radiation is given inside the body as close to the cancer as possible. Substances that produce radiation called radioisotopes may be injected into the blood, placed inside the rectum, or implanted directly into the tumor. Some of the radioactive implants are called "seeds" or "capsules." Internal radiation involves giving a higher dose of radiation in a shorter time span than with external radiation. Some internal radiation treatments stay in the body temporarily. Other internal treatments stay in the body permanently, though the radioactive substance loses its radiation within a short period of time. In some cases, both internal and external radiation therapies are used.

• 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 can increase the survival rate for patients with some stages of colon cancer. Chemotherapy can also help slow the growth or relieve symptoms of advanced cancer.

• Targeted Therapy 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 and help people live longer.