Colon Cancer

Description:

Alternative Names: Colorectal cancer; Cancer – colon.

Colorectal cancer is a type of uncontrolled growth of abnormal cells that can develop in the colon, rectum or both. Together, the colon and rectum make up the large intestine (also called the large bowel). The large intestine carries the remnants of digested food from the small intestine and eliminates them as waste through the anus.

Colorectal tumors begin as small growths (polyps) on the inside of the large intestine. Polyps that aren’t removed eventually can become cancerous, break through the wall of the colon or rectum, and spread to other areas.

Colon cancer is a common type of cancer in the United States. It is the second most common cause of death from cancer in the country. The American Cancer Society estimates that about 145,000 new cases of colorectal cancer are diagnosed each year, and about 56,000 people in the United States die of this disease each year.

The comparison of Colon cancer incidence in various countries strongly suggests that sedentarity, overeating (i.e., high caloric intake), and perhaps a diet high in meat (red or processed) could increase the risk of colorectal cancer. In contrast, a healthy body weight, physical fitness, and good nutrition decreases cancer risk in general. Accordingly, lifestyle changes could decrease the risk of colorectal cancer as much as 60-80%.

A high intake of dietary fiber (from eating fruits, vegetables, cereals, and other high fiber food products) has, until recently, been thought to reduce the risk of colorectal cancer and adenoma. In the largest study ever to examine this theory (88,757 subjects tracked over 16 years), it has been found that a fiber rich diet does not reduce the risk of colon cancer. A 2005 meta-analysis study further supports these findings.

The Harvard School of Public Health states: “Health Effects of Eating Fiber: Long heralded as part of a healthy diet, fiber appears to reduce the risk of developing various conditions, including heart disease, diabetes, diverticular disease, and constipation. Despite what many people may think, however, fiber probably has little, if any effect on colon cancer risk.”

Symptoms:

When an illness affects the colon or rectum, a number of symptoms can appear. The ones listed below are warning signs of a possible problem:

Diarrhea or constipation.

• Change in bowel habits.
• Blood in or on the stool (either bright red or very dark in color).
• Narrow stools.
• General stomach discomfort (bloating, fullness, and/or cramps).
• Frequent gas pains.
• Feeling that the bowel does not empty completely.
• Weight loss with no known reason.
• Anemia.

Causes and Risk factors:

In most cases of colon or rectal cancers, the cause or causes are unknown. Defects in genes that normally protect against cancer play the major role in causing polyp cells to continuously spread and become cancerous. Some of these cases are caused by inherited genetic defects, and such patients usually have family histories of colorectal cancer. Most of the genetic mutations involved in colon cancers, however, appear to arise spontaneously (no strong family history) rather than being inherited. In such cases, environmental or other factors trigger genetic changes in the intestine that lead to cancer.

Inherited Genetic Factors: A small percentage of cases of colon cancer are due to inherited factors. The two most common colorectal cancer syndromes associated with genetic mutations are familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer (HNPCC). Genetic tests can help screen for mutations associated with these syndromes.

Familial Adenomatous Polyposis (FAP): Familial adenomatous polyposis is caused by mutations in a tumor suppressor gene called APC. When the adenomatous polyposis coli (APC) gene is normal, it helps suppress tumor growth. In its defective form, it accelerates cell growth leading to polyps. The APC mutation can be inherited from either parent. People with FAP develop hundreds to thousands of polyps to in the colon. FAP causes less than 1% of all cases of colorectal cancer. If FAP is left untreated, however, virtually everyone who inherits this condition develops cancer by age 45. Polyps usually first appear when people with FAP are in their mid-teens. FAP also increases the risks for other types of cancers including stomach, thyroid, pancreatic, liver, and small intestine cancers.

Hereditary Nonpolyposis Colorectal Cancer (HNPCC): Hereditary nonpolyposis colorectal cancer (HNPCC), also known as Lynch syndrome, accounts for 3 – 5% of all colorectal cancers. About 50 – 80% of people who inherit the abnormal gene develop colon cancer by age 45. HNPCC is caused by mutations in MLH1, MSH2, MSH6, and PMS2 genes. People with HNPCC are prone to other cancers, including uterine and ovarian cancers, as well as cancers of the small intestine, liver, urinary tract, and central nervous system.

Risk Factors: Colorectal cancer is the third most common cancer in the U.S., with Americans facing a lifetime chance of 5 – 6% for this cancer. Men and women are at equal risk. Each year, about 108,000 Americans are diagnosed with colorectal cancer, and about 50,000 people die from the disease. About 73% of cancers occur in the colon and 27% in the rectum.

Age: Colorectal cancer risk increases with age. More than 90% of these cancers occur in people over age 50.

Race and Ethnicity: African-Americans have the highest risk of being diagnosed with, and dying from, colorectal cancer. Among Caucasians, Jews of Eastern European (Ashkenazi) descent have a higher rate of colorectal cancer. Asian Americans/Pacific Islanders, Hispanics/Latinos, and American Indians/Alaska Natives have a lower risk than Caucasians.

Family History of Colorectal Cancer: About 20 – 25% of colorectal cancers occur among people with a family history of the disease. (Seventy-five percent of cases are due to other causes.) People who have more than one first-degree relative (sibling or parent) with the disease are especially at high risk. The risk is even higher if the relative was diagnosed with colorectal cancer before the age of 60.

About 5 – 10% of patients with colorectal cancer have an inherited genetic abnormality that causes the disease. Syndromes associated with genetic mutations include familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer.

Dietary Factors: A diet high in red and processed meats increases the risk for colorectal cancer. Diets high in fruits and vegetables appear to be associated with reduced risk. It is not clear whether fiber consumption affects colorectal cancer risk. It is also not clear whether there is an association between colorectal cancer risk and vitamin deficiencies such as folic acid, a type of vitamin B. Recent studies have not shown that taking folic acid supplements lowers the risk of developing colorectal cancer.

Alcohol and Smoking: Alcohol use and smoking are associated with an increased risk for colorectal cancer. Patients who smoke and drink may also be diagnosed with Colon cancerat a younger age than non-drinkers and non-smokers.

Obesity: Obesity is associated with an increased risk for colorectal cancer, especially for men.

Physical Inactivity: A sedentary lifestyle increases the risk of developing colorectal cancer. Regular exercise may help reduce risk.

Diagnosis:

Colon and rectal cancers can be detected early using the screening tests discussed below. These tests can find precancerous polyps and colorectal cancers at stages early enough for complete removal and cure.

A doctor makes a diagnosis of colorectal cancer based on results of several types of tests. These tests include:

Biopsy: During a colonoscopy, the doctor can remove a tissue sample, which is sent to a laboratory for testing. A biopsy is the only way to definitively diagnose Colon cancer.

Blood Tests: Blood tests are used to evaluate the red blood cell count and check for anemia. The presence of anemia without any other obvious cause being present will usually require further evaluation of the gastrointestinal tract for a possible cancer. Blood tests are also used to check for specific tumor markers, substances that are released into the blood from cancer cells. Tumor markers include carcinoembryonic antigen (CEA) and CA 19-9. These tests may help your physician follow you for recurrences of colon cancer after treatment. By themselves, they cannot diagnose cancer and are not used as a screening test.

Imaging Tests: Various types of imaging tests can help detect the presence of Colon cancer or find out how far the cancer has spread. These tests include ultrasound, chest x-ray, magnetic resonance imaging (MRI) scan, positron emission tomography (PET) scan, and computed tomography (CT) scan.

Screening tests include:

Colonoscopy: Colonoscopy allows a doctor to view the entire length of the large intestine using a colonoscope, which is inserted into the rectum and snaked through the intestine. A colonoscope is a long, flexible tube that has a video camera one end. The doctor views images from the colonoscope on a display monitor. The test takes about 30 minutes to perform. If polyps are found, the doctor will remove them. The patient is given a sedative prior to the test, which produces a comfortable “twilight” sleep.

In order for the doctor to perform a successful colonoscopy, the colon and rectum must be completely empty. Your doctor will give you complete instructions for how to prepare during the days preceding the tests, and specific foods and liquids to avoid eating and drinking. The day before the test you will be given laxative solution to clean out the colon. Many people find this cleansing more unpleasant than the colonoscopy itself.

Colonoscopy is generally a safe procedure. In very rare cases, complications such as bowel perforation can occur.

Flexible Sigmoidoscopy: Sigmoidoscopy is similar to colonoscopy but only examines the rectum and the lower two feet of the colon. (In contrast, colonoscopy allows the doctor to view the entire colon.) The procedure takes about 10 – 20 minutes, and sedation is optional. Preparation procedures are less demanding than those for colonoscopy.

Double-Contrast Barium Enema (DCBE): The double-contrast barium enema test uses an x-ray to image the entire large intestine. The test takes about 30 – 45 minutes, and sedation is not required. Preparations are similar to those for colonoscopy and sigmoidoscopy. For the test, barium sulfate is inserted into the rectum using a small, flexible tube. The colon is then pumped with air to help the barium spread through the colon. If polyps are detected in the x-ray, your doctor may recommend you have a colonoscopy for further investigation and removal.

Virtual Colonoscopy: Virtual colonoscopy, also called CT colonoscopy, uses a computed tomography (CT) scan to take three-dimensional images of the colon. The test takes only 10 minutes to perform, and does not require sedation. (It does require the same preparations as other procedures to clean out the colon and bowel.) Air is pumped into the rectum through a small flexible tube. The patient is then slid into a CT scanner, which takes rapid images. Recent studies indicate that CT colonoscopy has a high accuracy rate in detecting adenomas and cancers.

Fecal Occult Blood Test (FOBT): A fecal occult blood test is a take-home test that uses stool samples to detect hidden (occult) blood in feces. It may detect small amounts of blood in your stool from polyps or a tumor, even when your stools appear normal. Your doctor will give you a kit with instructions on how to take stool samples and prepare them for the kit. Your doctor will also inform you about what medications and foods need to be avoided in the days prior to the test. The test kit and samples are sent to a laboratory and results usually come back in a few weeks. If blood is found in the stool samples, you will need to have a colonoscopy.

Fecal Immunochemical Test (FIT). The fecal immunochemical test is a newer type of take-home test for hidden (occult) blood. The test is similar to the fecal occult blood test, but patients do not need to follow medication or dietary restrictions. As with the FOBT, a colonoscopy is recommended if blood is found in the stool.

Stool DNA Test: Like the FIT and the FOBT, the stool DNA test is conducted at home and uses fecal samples. Instead of testing for the presence of blood, this test looks for abnormalities in genetic material that come from cancer or polyp cells. These genetic changes are found in genes such as APC, K-ras, and p53. If DNA mutations are found, a colonoscopy is needed. The stool DNA test is new, and is not yet widely available. Some insurance carriers may not cover its testing.

Treatment:

Treatment for Colon cancer includes surgery, chemotherapy, and radiation. These treatment methods may be combined.

Surgery is used for early-stage colorectal cancer. Usually, the tumor is removed along with part of the colon and nearby lymph nodes. Chemotherapy may be given after surgery to kill any remaining cancer cells. It may also be given along with radiation before surgery to reduce tumor size. Radiation therapy is not usually used in early-stage colorectal cancer, but is commonly used to treat early-stage rectal cancer. It is often combined with chemotherapy. Clinical trials are available for individual stages of colorectal cancer.

There are several methods for staging colorectal cancer. The older system, known as Dukes’, categorizes four basic stages: A, B, C, and D. The newer TMN system evaluates the tumor (T), lymph node (N), and how far the cancer has spread or metastasized (M). The results of TMN are combined to determine the stage of the cancer.

Colon cancer stages and treatment options are: Stage 0 (Carcinoma in situ).

In stage 0, cancer cells are fully contained in the innermost lining (mucosa) of the colon or rectum, and have not yet invaded the wall of the colon Treatment for stage 0 cancer usually involves surgical removal of the polyp (polypectomy) during colonoscopy.

Stage I: In stage I, the Colon cancer has spread through the mucosa of the colon wall into middle layers of tissue. Treatment for stage I involves resection of the tumor. The tumor may be removed along with part of the colon (colectomy).

Stage II: In stage IIA, Colon cancer has spread beyond the middle layers to the outer tissues of the colon or rectum. In stage IIB, the cancer has penetrated through the colon or rectum wall into nearby tissue or organs. Treatment for stage II cancer involves surgical resection. Chemotherapy after surgery (adjuvant chemotherapy) plus radiation is considered standard treatment for stage II rectal cancer, but is under debate for stage II colon cancer. Current guidelines recommend that the FOLFOX regimen (5-FU, leucovorin, oxaliplatin) be reserved for patients with high- or intermediate-risk stage II colon cancer, but not for good- or average-risk stage II cancer.

Stage III: In stage III, lymph nodes are involved but not distant sites. Stage IIIA and IIIB cancer has spread to as many as 3 lymph nodes. Stage IIIC Colon cancer involves 4 or more lymph nodes. Treatment for stage III colon cancer involves surgery and adjuvant chemotherapy with the FOLFOX regimen (5-FU, leucovorin, oxaliplatin). For patients with stage III rectal cancer, treatment includes chemotherapy and radiation, either before or following surgery.

Stage IV:

• Stage IV is metastasized cancer. The cancer has spread to nearby lymph nodes and to other organs of the body such as the liver or lungs.
• Treatment for stage IV cancer may sometimes include surgery. When cancer has spread, surgery to remove or bypass obstructions in the intestine may be performed. In these circumstances, surgery is considered palliative in that it may improve symptoms but will not lead to cure. In some cases, surgery may also be performed to remove tumors in areas that the cancer has spread, such as the liver, ovaries, or lung.
• Chemotherapy is standard treatment for metastasizedColon cancer. In advanced colorectal cancer, chemotherapy is either given directly into the arteries of the liver when it is involved or intravenously (through a vein) with 5-FU and leucovorin. The targeted therapy biologic drug bevacizumab may also be added. Other alternative chemotherapy choices are capecitabine, or irinotecan combined with cetuximab. Radiation therapy may be used in place of chemotherapy or in combination with it. Studies indicate that chemotherapy offers only a modest improvement in survival, but may help reduce symptoms.

Surgery with Colon cancer: Surgery is the most common treatment for all stages (Stage 0 – Recurrent) of colorectal cancer. The location and size of the tumor determines the type of surgical procedure to be done. The types of procedures include a polypectomy, colectomy or colostomy.

Polypectomy is the removal of a polyp using either a sigmoidoscope or colonoscope to locate the growth and another surgical instrument to remove the polyp. Polypectomy is sufficient for some benign polyps and some cases of carcinoma in situ, but surgery (i.e., colectomy) is recommended for true colon cancer.

Colectomy is the removal of part of the colon or rectum (whichever is cancerous) and a small amount of surrounding healthy tissue. The healthy parts of the colon or rectum are then sewn back together. This part of the surgery is called anastomosis. Additionally, during this procedure, the doctor will take out lymph nodes near the intestine and examine them for cancerous growth.

Colostomy is done if, after the portions of the colon, rectum and tissue are removed, the healthy tissues cannot be sewn back together. In this procedure, part of the colon is brought through an incision in the abdominal wall and formed into an artificial opening (stoma) to allow the discharge of feces into a lightweight bag attached to the skin. A colostomy may be temporary or permanent. A temporary colostomy is sometimes needed to allow the lower colon or the rectum to heal after surgery. Later, in a second surgery, the doctor reconnects the healthy sections of the colon or rectum. A permanent colostomy may be necessary when the tumor is in the rectum, and in very few cases, in the lower colon.

Radiation Therapy: In radiation therapy (also called x-ray therapy, radiotherapy, cobalt treatment or irradiation), high-energy rays are used to stop the cancer cells from growing and multiplying. Radiation therapy is sometimes used before surgery to shrink the tumor. More often, it is used after surgery to destroy any cancer cells that may remain or to relieve pain.

Radiation may come from a machine outside of the body (called external radiation therapy) or from putting radioactive materials through thin plastic tubes into the intestinal area (called internal radiation therapy).

Radiation therapy may be used in combination with surgery to treat Stage II – IV colorectal cancer. Chemotherapy or radiation therapy with surgery may be used to treat recurrent colorectal cancer. Colon cancer rarely requires radiation therapy after surgery; patients with rectal cancer are often offered radiation therapy after surgery to avoid the tumor coming back in the area it was excised.

The following preventive measures appear to reduce the risk of developing Colon cancer:

Eat a diet low in fat and high in fiber (25 g per day).

• Consume at least 1,000 mg of calcium each day.
• Eat foods that contain antioxidants, such as citrus fruits and dark-green and yellow vegetables.
• Exercise at least 30 minutes most days of the week.
• Stop smoking.
• Limit alcohol consumption. Older adults should consume no more then equivalent to one glass of wine daily.
• Have polyps and adenomas surgically removed upon discovery.

Medicine and medications:

Seven drugs are currently approved for Colon cancer chemotherapy:

5-fluorouracil (5-FU, Adrucil), which is often given in combination with leucovorin (Wellcovorin). Leucovorin is a vitamin that helps boost the effectiveness of 5-FU.

• Capecitabine (Xeloda).
• Oxaliplatin (Eloxatin).
• Irinotecan (Camptosar).
• Bevacizumab (Avastin).
• Cetuximab (Erbitux).
• Panitumumab (Vectibix).

Side effects occur with all chemotherapeutic drugs. They are more severe with higher doses and increase over the course of treatment.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.