Colon cancer is cancer of the large intestine (colon), the lower part of your digestive system. Rectal cancer is cancer of the last 6 inches of the colon. Together, they're often referred to as colorectal cancers. About 112,000 people are diagnosed with colon cancer annually, and about 41,000 new cases of rectal cancer are diagnosed each year, according to the American Cancer Society.
Most cases of colon cancer begin as small, noncancerous (benign) clumps of cells called adenomatous polyps. Over time some of these polyps become colon cancers.
Polyps may be small and produce few, if any, symptoms. Regular screening tests can help prevent colon cancer by identifying polyps before they become cancerous. If signs and symptoms of colon cancer do appear, they may include changes in bowel habits, blood in your stool, persistent cramping, gas or abdominal pain.
Symptoms
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 colon cancer include : -
A change in your bowel habits, including diarrhea or constipation or a change in the consistency of your stool for more than a couple of weeks
Rectal bleeding or blood in your stool
Persistent abdominal discomfort, such as cramps, gas or pain
Abdominal pain with a bowel movement
A feeling that your bowel doesn't empty completely
Weakness or fatigue
Unexplained weight loss
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.
Causes
Colorectal cancer
Precancerous colon lesions
Small colon polyps
Large colon polyp
Colon cancer
In general, cancer occurs when healthy cells become altered. Healthy cells grow and divide in an orderly way to keep your body functioning normally. But sometimes this growth gets out of control - cells continue dividing even when new cells aren't needed. In the colon and rectum, this exaggerated growth may cause precancerous cells to form in the lining of your intestine.
Over a long period of time - spanning up to several years - some of these areas of abnormal cells may become cancerous. In later stages of the disease, colon cancer may penetrate the colon walls and spread (metastasize) to nearby lymph nodes or other organs. As with most cancers, the exact cause for colon cancer is unknown.
Precancerous growths in the colon
Precancerous cells can occur anywhere in your large intestine, the muscular tube that forms the last part of your gastrointestinal tract. The colon comprises the upper 4 to 5 feet of your large intestine, and the rectum makes up the lower 6 inches.
Precancerous growths most commonly occur as clumps of cells (polyps) that extend from the wall of the colon. Polyps can appear mushroom-shaped. Precancerous growths can also be flat or recessed into the wall of the colon (nonpolypoid lesions). Nonpolypoid lesions are more difficult to detect, but are less common.
Several types of colon polyps exist. Among the most common are : -
Adenomas : - These polyps have the potential to become cancerous and are usually removed during screening tests such as flexible sigmoidoscopy or colonoscopy.
Hyperplastic polyps : - These polyps are rarely, if ever, a risk factor for colorectal cancer.
Inflammatory polyps : - These polyps may follow a bout of ulcerative colitis. Some inflammatory polyps may become cancerous, so having ulcerative colitis increases your overall risk of colon cancer.
Risk factors
Factors that may increase your risk of colon cancer include : -
Age : - About 90 percent of people diagnosed with colon cancer are older than 50. Colon cancer can occur in younger people, but it occurs much less frequently.
A personal history of colorectal cancer or polyps : - If you've already had colon cancer or adenomatous polyps, you have a greater risk of colon cancer in the future.
Inflammatory intestinal conditions : - Long-standing inflammatory diseases of the colon, such as ulcerative colitis and Crohn's disease, can increase your risk of colon cancer.
Inherited disorders that affect the colon : - Genetic syndromes passed through generations of your family can increase your risk of colon cancer. These syndromes cause only about 5 percent of all colon cancers. One genetic syndrome called familial adenomatous polyposis (FAP) is a rare disorder that causes you to develop thousands of polyps in the lining of your colon and rectum.
People with untreated FAP have a greater than 90 percent chance of developing colon cancer by age 45. Another genetic syndrome, hereditary nonpolyposis colorectal cancer (HNPCC), also called Lynch syndrome, is more common than FAP. People with HNPCC have an increased risk of colon cancer and tend to develop colon cancer at an early age. Both FAP and HNPCC can be detected through genetic testing. Talk to your doctor about whether your family history suggests you have a risk of these conditions.
Family history of colon cancer and colon polyps : - You're more likely to develop colon cancer if you have a parent, sibling or child with the disease. If more than one family member has colon cancer or rectal cancer, your risk is even greater. In some cases, this connection may not be hereditary or genetic. Instead, cancers within the same family may result from shared exposure to an environmental carcinogen or from diet or lifestyle factors.
Diet : - Colon cancer and rectal cancer may be associated with a diet low in fiber and high in fat and calories. Research in this area has had mixed results. Some studies have found an increased risk of colon cancer in people who eat diets high in red meat and processed meats.
People who eat a diet similar to that of Western countries, such as the United States and Europe, have a higher risk of developing colon cancer than do people who eat diets typically seen in developing countries. When people move from a developing country to a Western country and adapt to the Western diet, their risk of colon cancer increases. Although many studies have tried to identify what part of the Western diet may cause colon cancer, the answer remains unknown.
A sedentary lifestyle : - If you're inactive, you're more likely to develop colon cancer. This may be because when you're inactive, waste stays in your colon longer. Getting regular physical activity may reduce your risk.
Diabetes : - People with diabetes and insulin resistance may have an increased risk of colon cancer.
Obesity : - People who are obese have an increased risk of colon cancer and an increased risk of dying of colon cancer when compared with people considered normal weight.
Smoking : - People who smoke cigarettes may have an increased risk of colon cancer. They may also have an increased chance of dying of colon cancer.
Alcohol : - Heavy use of alcohol may increase your odds of colon cancer.
Growth hormone disorder : - Acromegaly, an uncommon disorder that causes an excess of growth hormone in your body, may increase your risk of colon polyps and colon cancer.
Radiation therapy for cancer : - Radiation therapy directed at the abdomen to treat previous cancers may increase the risk of colon cancer.
When to seek medical advice
If you notice any symptoms of colon cancer, such as blood in your stool or a persistent change in bowel habits, see your doctor as soon as possible. Keep in mind that colorectal cancer can occur in younger as well as older people. If you're at high risk, don't wait until symptoms appear. See your doctor for regular screenings.
Talk to your doctor about when you should begin screening for colon cancer. Guidelines generally recommend colon cancer screenings begin at age 50. Your doctor may recommend more frequent or earlier screening if you have other risk factors, such as a family history of the disease.
Tests and diagnosis
Barium enema
Sigmoidoscopy
Colonoscopy
Stages of colon cancer
Screening
Most colon cancers develop from adenomatous polyps. Screening can detect polyps before they become cancerous. Screening may also detect colon cancer in its early stages when there is a good chance for cure.
You may be embarrassed by the screening procedures, worried about discomfort or afraid of the results. Discuss your screening options and your concerns with your doctor. Most procedures are only moderately uncomfortable, and working with a doctor you like and trust can help ease your embarrassment.
Common screening and diagnostic procedures include the following : -
Stool blood test : - The fecal occult (hidden) blood test checks a sample of your stool for blood. It can be performed in your doctor's office, but you're usually given a kit that explains how to take the sample at home. You return the sample to a lab or your doctor's office to be checked. Not all cancers can be detected with a stool blood test, since not all cancers bleed and those that do often bleed intermittently.
This can result in a negative test result, even though you may have cancer. If blood is detected in your stool, your doctor may order other screening tests to determine the source of the blood. Blood in your stool can be the result of hemorrhoids or an intestinal condition other than cancer. Certain foods also may alter test results, suggesting blood in the colon when there is none.
Stool DNA test : - This test involves analyzing several DNA markers, which come from cells that are shed by colon cancers or precancerous polyps into stool. To complete the stool DNA test, you typically receive a collection kit from your doctor, collect one bowel movement at home and then send the kit to a laboratory for analysis.
Stool DNA testing is thought to be more accurate for detecting colon cancer than polyps, and it's important to remember that this test can't detect all the possible DNA mutations that may indicate a tumor. This test isn't widely available yet, and it may not be covered by your insurance. For these reasons it's not commonly used.
Flexible sigmoidoscopy : - In this test, your doctor uses a flexible, slender and lighted tube to examine your rectum and sigmoid - approximately the last 2 feet of your colon. The test usually takes just a few minutes. It can sometimes be uncomfortable, and there's a slight risk of perforating the colon wall.
If a polyp or colon cancer is found during this exam, your doctor will recommend colonoscopy to look at the entire colon and remove any polyps that are present for examination under a microscope. Because sigmoidoscopy only examines the lower third of the colon, polyps or cancer in the rest of the colon won't be detected.
Barium enema : - This diagnostic test allows your doctor to evaluate your entire large intestine with an X-ray. Barium, a contrast dye, is placed into your bowel in an enema form. During a double-contrast barium enema, air is also added. The barium fills and coats the lining of the bowel, creating a clear silhouette of your rectum, colon and sometimes a small portion of your small intestine.
There's also a slight risk of perforating the colon wall, and the test has a significantly high rate of missing important lesions. A flexible sigmoidoscopy is often done in addition to the barium enema to aid in detecting small polyps that a barium enema X-ray may miss, especially in the lower bowel and rectum. Barium enema may miss small polyps or small cancers. If an abnormality is detected using barium enema, your doctor may recommend a colonoscopy.
Colonoscopy : - Colonoscopy is similar to flexible sigmoidoscopy, but the instrument used - a colonoscope, which is a long, flexible and slender tube attached to a video camera and monitor - allows your doctor to view your entire colon and rectum. If any polyps are found during the exam, your doctor may remove them immediately or take tissue samples (biopsies) for analysis. This is done through the colonoscope and is painless.
You may receive a mild sedative to make you more comfortable. Preparation for the procedure involves drinking a large amount of fluid containing a laxative to clean out your colon - enemas are no longer necessary. Major risks of diagnostic colonoscopy include bleeding and perforation of the colon wall, but these are rare.
Virtual colonoscopy (CT colonography) : - Though not available at all medical centers, virtual colonoscopy may be one screening option. Virtual colonoscopy uses a computerized tomography (CT) machine to take images of your colon, rather than using a scope inserted in your rectum to see inside your colon. Virtual colonoscopy still requires that you undergo a bowel preparation to remove any stool. If any abnormalities are detected on virtual colonoscopy, you'll still need to undergo conventional colonoscopy. Research into virtual colonoscopy is still ongoing.
Diagnosis
If your doctor suspects you may have colon cancer based on your signs and symptoms, he or she may recommend colonoscopy to look for colon cancer. Colonoscopy allows your doctor to look for polyps or unusual areas in your colon. Your doctor can also remove a sample of tissue from your colon to look for cancer cells. In some cases, barium enema or flexible sigmoidoscopy may be used to diagnose colon cancer.
Staging your cancer
Once you've been diagnosed with colon cancer, your doctor will then order tests to determine the extent, or stage, of your cancer. Staging helps determine what treatments are most appropriate for you. Staging tests may include imaging procedures such as abdominal CT scan or chest X-ray.
The stages of colon cancer are : -
Stage 0 : - Your cancer is in the earliest stage. It hasn't grown beyond the inner layer (mucosa) of your colon or rectum. This stage of cancer may also be called carcinoma in situation.
Stage I : - Your cancer has grown through the mucosa but hasn't spread beyond the colon wall or rectum.
Stage II : - Your cancer has grown into or through the wall of the colon or rectum but hasn't spread to nearby lymph nodes.
Stage III : - Your cancer has invaded nearby lymph nodes but isn't affecting other parts of your body yet.
Stage IV : - Your cancer has spread to distant sites, such as other organs - for instance to your liver or lung, to the membrane lining the abdominal cavity, or to an ovary.
Recurrent : - This means your cancer has come back after treatment. It may recur in your colon, rectum or other part of your body.
Treatments and drugs
The type of treatment your doctor recommends will depend largely on the stage of your cancer. The three primary treatment options are: surgery, chemotherapy and radiation.
Surgery (colectomy) is the main treatment for colorectal cancer. How much of your colon is removed and whether other therapies, such as radiation or chemotherapy, are an option for you depend on the location of your cancer, how far cancer has penetrated into the wall of your bowel, and whether it has spread to your lymph nodes or other parts of your body.
[ Colectomy ]
[ Colostomy ]
Surgical procedures
Your surgeon removes the part of your colon that contains the cancer, along with a margin of normal tissue on either side of the cancer to help ensure that no cancer is left behind. Nearby lymph nodes are usually also removed and tested for cancer. Your surgeon is often able to reconnect the healthy portions of your colon or rectum. But when that's not possible, for instance if the cancer is at the outlet of your rectum, you may need to have a permanent or temporary colostomy. This involves creating an opening in the wall of your abdomen from a portion of the remaining bowel for the elimination of body waste into a special bag. Sometimes the colostomy is only temporary, allowing your colon or rectum time to heal after surgery. In some cases, however, the colostomy may be permanent.
Side effects of colon cancer surgery may include short-term pain and tenderness, and temporary constipation or diarrhea. If you have a colostomy, you may develop an irritation on the skin around the opening (stoma).
Surgery to prevent cancer
In cases of rare, inherited syndromes such as familial adenomatous polyposis, or inflammatory bowel disease such as ulcerative colitis, your doctor may recommend removal your entire colon and rectum in order to prevent cancer from occurring in the future. Then, in a procedure known as ileal pouch-anal anastomosis, your surgeon will likely construct a pouch from the end of your small intestine that attaches directly to your anus. This allows you to expel waste normally, although you may have several watery bowel movements a day.
Surgery for early-stage cancer
If your cancer is small, localized in a polyp and in a very early stage, your surgeon may be able to remove it completely during a colonoscopy. If the pathologist determines that the cancer in the polyp doesn't involve the base - where the polyp is attached to the bowel wall - then there's a good chance that the cancer has been completely eliminated.
Some larger polyps may be removed using laparoscopic surgery. In this procedure, your surgeon performs the operation through several small incisions in your abdominal wall, inserting instruments with attached cameras that display your colon on a video monitor. He or she may also take samples from the lymph nodes that drain the area where the cancer is located. Studies have found that people undergoing this procedure need less pain medication and leave the hospital a day earlier on average. Also, people who have this procedure don't have higher rates of recurrence than those who choose the open surgery.
Surgery for advanced cancer
If your cancer is very advanced or your overall health very poor, an operation to relieve a blockage of your colon or other conditions in order to improve your symptoms may be the best option. This type of surgery is referred to as palliative surgery. The goal of palliative surgery isn't to cure your cancer, but to relieve signs and symptoms, such as bleeding and pain.
In specific cases where the cancer has spread only to the liver and if your overall health is otherwise good, your doctor may recommend surgery to remove the cancerous lesion from your liver. Chemotherapy may be used before or after this type of surgery. This treatment may improve your prognosis.
Chemotherapy
Chemotherapy uses drugs to destroy cancer cells. Chemotherapy can be used to destroy cancer cells after surgery, to control tumor growth or to relieve symptoms of colon cancer. Your doctor may recommend chemotherapy if your cancer has spread beyond the wall of the colon. In some cases, chemotherapy is used along with radiation therapy.
Possible side effects of chemotherapy include nausea and vomiting, mouth sores, fatigue, hair loss and diarrhea. Discuss the side effects and risks as well as the potential benefits with your doctor.
Radiation therapy
Radiation therapy uses powerful energy sources, such as X-rays, to kill any cancer cells that might remain after surgery, to shrink large tumors before an operation so that they can be removed more easily, or to relieve symptoms of colon cancer and rectal cancer.
Radiation therapy is rarely used in early stage colon cancer, but is a routine part of treating early stage rectal cancer, especially if the cancer has penetrated through the wall of the rectum or traveled to nearby lymph nodes. Radiation therapy, usually combined with chemotherapy, may be used after surgery to reduce the risk that the cancer may recur in the area of the rectum where it began.
Side effects of radiation therapy may include diarrhea, rectal bleeding, fatigue, loss of appetite and nausea.
Targeted drug therapy
Three drugs that target specific defects that allow cancer cells to proliferate are available to people with advanced colon cancer. The drugs bevacizumab (Avastin), cetuximab (Erbitux) and panitumumab (Vectibix) can be given along with chemotherapy drugs or alone. Bevacizumab works to prevent tumors from developing new blood vessels, which can deliver the oxygen and nutrients cancers need to survive.
Cetuximab and panitumumab target a chemical signal that tells cells to divide and reproduce. Cetuximab was approved by the Food and Drug Administration in 2007 as a single-agent treatment for advanced colon cancer for which other treatments have failed. Panitumumab remains experimental.
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