Colon cancer is cancer that starts in the large intestine (the colon). It is a leading cause of cancer deaths in the United States, but regular screening and early diagnosis can lead to complete cure.
Colon Cancer Overview
Colon cancer is cancer that starts in the large intestine (the colon), which is the lower part of your digestive system. Rectal cancer is cancer of the last several inches of the colon. These cancers are similar and, together, they are often referred to as colorectal cancers.
The colon and the rectum are parts of the large intestine, which is the lower part of the body’s digestive system. During digestion, food moves through the stomach and small intestine into the colon. The colon absorbs water and nutrients from the food and stores waste matter (stool). Stool moves from the colon into the rectum before it leaves the body.
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. For this reason, doctors recommend regular screening tests to help prevent colon cancer by identifying polyps before they become colon cancer.
Many cases of colon cancer have no symptoms. If symptoms are present, they may include abdominal pain and tenderness in the lower abdomen, blood in the stool, diarrhea, constipation or other changed in bowel habits, and weight loss for no known reason.
Colorectal cancer is the third most common type of cancer in men and women in the United States. It is a leading cause of cancer death, but deaths from colorectal cancers have decreased in recent years with the widespread use of regular screenings, including colonoscopies and fecal occult blood tests, which check for blood in the stool.
Colon Cancer Symptoms
Many people with colon cancer experience no symptoms in the early stages of the disease. When symptoms appear, they will likely vary, depending on the cancer's size and location in your large intestine.
Signs and symptoms of colon cancer include:
- Changes in bowel habits, including diarrhea or constipation or a change in the consistency of stool
- Rectal bleeding or blood in the stool
- Persistent abdominal discomfort, such as cramps, gas, bloating, a feeling of fullness, or pain
- A feeling that your bowel does not empty completely
- Weakness or fatigue
- Unexplained weight loss
Colon Cancer Causes
In most cases, the cause of colon cancer is not clear. Doctors know that colon cancer occurs when healthy cells in the colon become altered. Healthy cells grow and divide in an orderly way to keep your body functioning normally. But when a cell is damaged and becomes cancerous, cells continue to divide, even when new cells are not needed. These cancer cells can invade and destroy normal tissue nearby, and cancerous cells can travel to other parts of the body.
Colon cancer most often begins as clumps of precancerous cells (polyps) on the inside lining of the colon. Polyps can appear mushroom-shaped, or they can be flat or recessed into the wall of the colon. Removing polyps before they become cancerous can prevent colon cancer.
Inherited gene mutations that increase the risk of colon cancer can be passed through families, but these inherited genes are linked to only a small percentage of colon cancers. Inherited gene mutations do not make cancer inevitable, but they can increase an individual's risk of developing cancer.
Factors that may increase your risk of colon cancer include:
- Older age. Most people diagnosed with colon cancer are older than 50 years. Colon cancer can occur in younger people, but it occurs much less frequently.
- African-American race. African-Americans have a greater risk of colon cancer than do people of other races.
- A personal history of colorectal cancer or polyps. If you have already had colon cancer or adenomatous polyps, you have a greater risk of colon cancer in the future.
- Inflammatory intestinal conditions. Chronic inflammatory diseases of the colon, such as ulcerative colitis and Crohn's disease, can increase your risk of colon cancer.
- Inherited syndromes that increase colon cancer risk. Genetic syndromes passed through generations of your family can increase your risk of colon cancer. These syndromes include familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer, which is also known as Lynch syndrome.
- Family history of colon cancer and colon polyps. You are 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.
- Low-fiber, high-fat diet. Colon cancer and rectal cancer may be associated with a diet low in fiber and high in fat and calories. Some studies have found an increased risk of colon cancer in people who eat diets high in red meat. Diets high in vegetables, fruits, and whole grains have been linked with a decreased risk of colorectal cancer, but fiber supplements do not seem to help. It is not clear if other dietary components (for example, certain types of fats) affect colorectal cancer risk.
- A sedentary lifestyle. If you are inactive, you are more likely to develop colon cancer. Getting regular physical activity may reduce your risk of colon cancer.
- Diabetes. People with diabetes and insulin resistance may have an increased risk of colon cancer.
- Obesity. People who are very overweight or 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.
- Alcohol. Heavy use of alcohol may increase your risk of colon cancer.
- Radiation therapy for cancer. Radiation therapy directed at the abdomen to treat previous cancers may increase the risk of colon cancer.
Colon Cancer Diagnosis
Regular screening can often find colorectal cancer early, when it is most likely to be curable. In many people, screening can also prevent colorectal cancer altogether. This is because some polyps, or growths, can be found and removed before they have the chance to turn into cancer.
Tests used to screen for colorectal cancers include:
- guaiac-based fecal occult blood test (gFOBT) and fecal immunochemical test (FIT). Samples of stool (feces) are checked for blood, which might be a sign of a polyp or cancer.
- stool DNA test. A sample of stool is checked for certain abnormal sections of DNA (genetic material) from cancer or polyp cells.
- sigmoidoscopy. A flexible, lighted tube is put into the rectum and lower colon to check for polyps and cancer.
- colonoscopy. A longer, flexible tube is used to look at the entire colon and rectum.
- double contrast barium enema. This is an x-ray test of the colon and rectum.
- CT colonography (virtual colonoscopy). This is a type of CT scan of the colon and rectum.
gFOBT, FIT, and stool DNA testing mainly find cancer, but they can also find polyps.
Sigmoidoscopy, colonoscopy, double contrast barium enema, and CT colonography are good at finding cancer and polyps. Polyps found before they become cancer can be removed, so these tests may prevent colorectal cancer. This is why these tests are preferred if they are available and you are willing to have them.
Once you have been diagnosed with colorectal cancer, your doctor will order tests to determine the extent (stage) of your cancer. Staging helps determine what treatments are most appropriate for you.
Staging tests may include imaging procedures such as abdominal and chest CT scans. In many cases, the stage of your cancer may not be determined until after colorectal cancer surgery.
The stages of colorectal cancer are:
- Stage I. The cancer has grown through the superficial lining (mucosa) of the colon or rectum but has not spread beyond the colon wall or rectum.
- Stage II. The cancer has grown into or through the wall of the colon or rectum but has not spread to nearby lymph nodes.
- Stage III. Your cancer has invaded nearby lymph nodes but is not affecting other parts of your body yet.
- Stage IV. Your cancer has spread to distant sites, such as your liver or lung.
Living With Colon Cancer
If you have or have had colon cancer, you can take steps to manage the stress that accompanies the diagnosis:
- Learn about colon cancer so you can make informed decisions about your care.
- Have a schedule of follow-up tests and go to each appointment.
- Take care of yourself so that you are ready to fight cancer. This includes eating a healthy that includes plenty of fruits, vegetables and whole grains, exercising for at least 30 minutes most days of the week, and getting enough sleep so that you wake feeling rested.
- Accept help and support from family and friends.
- Talk with other cancer survivors or attend support groups.
Colon Cancer Treatments
The type of treatment your doctor recommends will depend largely on the stage of your cancer. The 3 primary treatment options for colon cancer are surgery, chemotherapy, and radiation.
Surgery. If your cancer is small, localized in a polyp, and in a very early stage, your doctor may be able to remove it completely during a colonoscopy. Larger polyps may be removed using endoscopic mucosal resection. If the pathologist determines that it is likely that the cancer was completely removed, there may be no need for additional treatment.
Polyps that cannot be removed during colonoscopy 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. The surgeon may also take samples from lymph nodes in the area where the cancer is located.
If your colon cancer has grown into or through your colon, your surgeon may recommend a partial colectomy to remove the part of your colon that contains the cancer, along with a margin of normal tissue on either side of the cancer. Nearby lymph nodes are usually also removed and tested for cancer.
If your cancer is very advanced or your overall health very poor, your surgeon may recommend an operation to relieve a blockage of your colon or other conditions in order to improve your symptoms. This surgery is not done to cure cancer, but instead 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 for colon cancer is usually given after surgery if the cancer has spread to the lymph nodes. In this way, chemotherapy may help reduce the risk of cancer recurrence.
Chemotherapy can also be given to relieve symptoms of colon cancer that has spread to other areas of the body. Chemotherapy may be used before surgery to shrink the cancer before an operation. In people with rectal cancer, chemotherapy is typically used along with radiation therapy.
The following drugs are approved for use in colon cancer:
- Bevacizumab (Avastin)
- Capecitabine (Xeloda)
- Cetuximab (Erbitux)
- Fluorouracil (Adrucil, Efudex, Fluoroplex)
- Irinotecan Hydrochloride (Camptosar)
- Leucovorin Calcium (Wellcovorin)
- Oxaliplatin (Eloxatin)
- Panitumumab (Vectibix)
- Ramucirumab (Cyramza)
- Regorafenib (Stivarga)
- Ziv-Aflibercept (Zaltrap)
Radiation therapy. Radiation therapy uses powerful energy sources, such as X-rays, to kill 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. Radiation therapy, usually combined with chemotherapy, may be used after surgery to reduce the risk that the cancer may recur.
Targeted drug therapy. Drugs that target specific defects that allow cancer cells to grow are available to people with advanced colon cancer, including bevacizumab (Avastin), cetuximab (Erbitux), panitumumab (Vectibix) and regorafenib (Stivarga). Targeted drugs can be given along with chemotherapy or alone. Targeted drugs are typically reserved for people with advanced colon cancer.