Colorectal cancer

Definition

Colorectal cancer is a malignancy of the colon (bowel) and/or rectum. It is the second most common cause of cancer-related death in the United States, and is diagnosed in more than 130,000 new patients annually.

Description

Colorectal cancer occurs in either the last 6 ft (1.8 m) of intestine, known as the large bowel or colon, and/or in the rectum, where the colon terminates and waste (feces) leaves the body. The majority of malignancies that occur in colorectal cancers are called adenocarcinomas. When an individual develops colorectal adenocarcinomas, malignant cancer cells grow inside the colon and/or the rectum. Large clusters of these cells form structures known as tumors.

Causes & symptoms

Causes & risk factors

The exact cause of colorectal cancer is unknown. However, there are a number of known risk factors that increase the odds for developing the disease. They include:

• Family history. Individuals who have one or more close relatives that were diagnosed with colorectal cancer may be at increased risk for the disease. In 2003, research showed that about 5% of colorectal cancer patients had inherited syndromes.
• History of bowel disease and/or colon polyps. Certain types of colon polyps, which are tumor-like, benign outgrowths of tissue within the colon, may act as an early warning sign of or a precursor to colorectal cancer. They may develop into malignancies later in life. Colon diseases that cause inflammation and irritation of the bowel, such as Crohn's disease and inflammatory bowel disease, also can increase an individual's risk of developing a colorectal malignancy.
• Obesity. Overweight individuals, especially those with an apple-shaped body type (where fat is concentrated around the waist) as opposed to a pear-shaped body (where fat is stored in the hips and thighs), are at an increased risk for colorectal cancer. A high fat diet also increases an individual's chance of developing colorectal cancer.
• Age. Individuals over age 50 are at an increased risk for colorectal cancer.
• Sedentary lifestyle. A moderate exercise program is thought to have a preventive effect against cancer.
• Night work. A 2003 study showed that working the night shift actually may increase risk of colorectal cancer in women. Exposure to light at night suppresses the body's natural production of melatonin, a hormone that helps keep certain intestinal cancers from proliferating.

Symptoms

Symptoms of colorectal cancer include:

• blood on the rectum or in the stool
• feelings of fecal urgency (feeling as if one has to have a bowel movement all the time)
• stomach and/or abdominal pain
• changes in bowel habits, including constipation, diarrhea, and/or pencil-thin stools
• extreme fatigue
• decreased appetite

Diagnosis

The simplest screening tests for colorectal cancer include a digital rectal exam and a fecal occult blood test (FOBT). In the digital rectal exam, a physician inserts a gloved finger into the rectum and feels for any irregularities. In the FOBT, stool samples are tested for traces of blood. The test can be done at home and sent to a lab for analysis. FOBT can reduce the death rate by about 33%. Unfortunately, in the United States, over the past six years less than 35% of the population had received a FOBT.

A flexible sigmoidoscopy and/or a colonoscopy may be performed to view the interior of the colon. The former examines the rectum and lower colon for cancer, and the latter examines the full length of the colon. During these procedures, a doctor passes a flexible tube with a

tiny, fiber-optic camera device (an endoscope) through the rectum and into the colon. The doctor can carefully examine the lining of the intestine for signs of cancer. A tissue sample (a biopsy) of the colon also can be taken through the endoscope to examine under a microscope for evidence of malignancy. Both tests can cause discomfort, and may be done under a local anesthetic if desired.

A lower GI (gastrointestinal) x-ray series can be helpful in determining how much of the intestine is involved in the disease. A chalky solution called barium, which acts as a contrast agent to illuminate the gastrointestinal tract on x-ray film, is administered in enema form to the patient. In some cases, air also is pumped into the rectum to provide a clearer view of the large intestine. This is called a double-contrast barium enema. The pressure in the patient's abdomen from the air and barium contrast likely will cause some discomfort.

After colorectal cancer is diagnosed, further testing is required to determine how far the cancer has spread. This procedure is known as staging. There are five different stages of colorectal cancer:

• Stage 0 (carcinoma in situ). This is the earliest stage of colorectal cancer, and indicates that cancerous cells have not spread beyond the colon lining.
• Stage I. The cancer has spread to the second and third layers of the inside wall of the colon, but is still contained within the colon.
• Stage II. The cancer has spread beyond the colon, but has not spread to the lymph nodes.
• Stage III. The cancer has spread to a nearby lymph node, but has not spread throughout the body.
• Stage IV. The cancer has spread throughout the body.

There is a sixth subtype of cancer, called recurrent, which is used to classify colorectal cancer that was treated, seemed to resolve, and has now recurred either in the colon or in another part of the body.

Treatment

The best chance for successful treatment is to detect colorectal cancer early. Colorectal cancer is a life-threatening disease, and a correct diagnosis and appropriate treatment with surgery, chemotherapy, and/or radiation is critical to controlling the illness.

Acupuncture and guided imagery may be useful tools in treating pain symptoms and improving immune function associated with colorectal cancer. Acupuncture involves the placement of a series of thin needles into the skin at targeted locations on the body, known as acupoints, in order to harmonize the energy flow within the human body.

Guided imagery involves creating a visual mental image of pain as a means of relaxation. Once the pain can be visualized, the patient can adjust the image to make it more pleasing, and thus more manageable, to them.

Movement therapies, such as yoga, t'ai chi, and qigong can aid the recovering patient. They may lessen pain symptoms, and help the person to relax and reduce stress.

A number of herbal remedies also are available to lessen pain symptoms and promote relaxation and healing. However, cancer patients should consult with their healthcare professional before taking them. Depending on the preparation and the type of herb, these remedies may interact with or enhance the effects of other prescribed medications. Herbs that promote healing of the digestive tract include slippery elm bark (Ulmus rubra), marsh mallow root (Althaea officinalis), and goldenseal (Hydrastis canadensis).

Allopathic treatment

Treatment options include surgery, chemotherapy, and radiation. Colorectal cancer is treated in two ways, locally to eliminate tumor cells from the colon by surgery and radiation, and to systemically destroy cancer cells that have traveled to other parts of the body. Systemic therapy includes the use of chemotherapy drugs.

Surgery

The extent of surgery depends on the type of colorectal cancer, whether the disease has spread, and the patient's age and health. A surgical procedure known as a bowel resection is performed for colon cancers, where the length of colon containing the cancerous cells is removed, along with nearby tissues and lymph nodes. The two ends of the remaining colon are then sewn back together.

For cancer affecting the rectum, several other surgical methods may be employed, including local excision of the cancer (where cancerous cells and nearby tissues are cut out of the rectum) and transanal resection, where invasive cancerous tissue is removed along with normal anal tissue.

Depending on the stage of the cancer and the degree of surgery required, some patients may need to get a colostomy. A colostomy involves surgically attaching the bowel to an opening in the abdominal wall where waste is eliminated into an attached bag.

The presence of cancer cells in the lymph nodes may require more extensive surgery. If the cancer has spread to the nodes, the patient will need either radiation, chemotherapy, hormone therapy, or a combination of all three after surgery. This is called "adjuvant therapy."

Radiation

Once the cancer has been removed, the doctor may recommend radiation treatment to destroy any remaining cancer cells. In cases where the cancer is located in hard to reach areas, radiation may be used to shrink the cancer growth or tumor. Radiation stops the cancer cells from dividing. It works especially well on fast-growing tumors. Unfortunately, it also stops some types of healthy cells from dividing. Healthy cells that divide quickly, like those of the skin and hair, are affected the most. This is why radiation can cause fatigue, skin problems, and hair loss.

Radiation therapy can be internal, where particles of radioactive materials are implanted into a tumor, or external, where energy rays (radiation) are directed at the cancer from outside the body. External radiation, the most common type of treatment for colorectal cancer, is usually administered five days a week for several weeks. Recent studies indicate that radiation therapy decreases the likelihood of local recurrence of colorectal cancer by a significant margin. Some clinicians argue that the therapy is most effective when given before surgery rather than after. No definitive clinical trials proved the most effective timing as of late 2001.

Chemotherapy

Colorectal cancer surgery may be followed by chemotherapy in even the earliest stages. Chemotherapy is administered either orally or by injection into a blood vessel. It is usually given in cycles, followed by a period of time for recovery, followed by another course of drugs. Treatment time may range between four and nine months. In the fall of 2001, the Food and Drug Administration (FDA) approved trials for a new vaccine to help treat colorectal cancer. Investigators planned to give the vaccine in conjunction with chemotherapy to help prevent recurrentce of the disease. In 2003, the FDA approved a new chemotherapy drug called Avastin to help fight metastatic spread of colorectal cancer.

Some types of chemotherapy produce significant side effects, including nausea and vomiting, temporary hair loss, mouth sores, skin rashes, fatigue, a weakened immune system, and infertility. However, most side effects are temporary and disappear once treatment has ended.

Expected results

According to the American Cancer Society, colorectal cancers cause more than 56,000 deaths each year in the United States. However, the death rate for the disease has declined steadily over the past several decades, and since 1985, annual deaths due to colorectal cancer have declined at an average rate of 1.6% per year. Early detection is key to improved survival; patients with colorectal cancers detected early (at stage I) have a 96% survival rate. In comparison, patients who are diagnosed with stage IV colorectal cancer only have a 5% survival rate.

Prevention

Proper diet and exercise have been shown to help prevent many types of cancers, including colorectal cancer. Research published in 2003 confirmed the benefits of physical activity in reducing risk of colon and rectal cancers. A well-balanced diet consisting of a minimum of five servings of fruits and vegetables and six servings of food from other plant sources (i.e., cereals, grains, pastas) is recommended by the American Cancer Society. Additionally, patients may opt for a diet of whole foods. A number of fruits and vegetables have been shown to have antioxidant properties, and may be useful in preventing cancer. These include carotenoids, which are found in fruit pigments; flavenoids found in vegetable pigments; and particularly, lycopene, which is found in tomato juice.

Recent clinical studies also have indicated that regular use of green tea (produced from the Camellia sinensis plant) may reduce the risk of certain types of cancer, including colorectal cancers. Green tea contains polyphenols, an antioxidant substance that also may inhibit the growth of existing cancer cells. In some animal studies, injections of tea extracts reduced the size of cancerous tumors. The antioxidant effects of green tea need to be studied further to more clearly define the role of the herb in cancer treatment and prevention.

Because early detection is so critical to recovery from colorectal cancer, patients considered "at risk" for the disease due to genetic, lifestyle, or environmental factors should undergo regular screening after age 50 (and possibly before, depending on the individual's personal and medical history). The American Cancer Society recommends the following screening tests:

• an annual FOBT plus a flexible sigmoidoscopy every five years
• a colonoscopy every 10 years
• a double contrast barium enema every five to 10 years

A digital rectal exam also is recommended during each screening session.

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