Colon cancer is cancer of the large intestine (colon), the lower part of your digestive system. Rectal cancer is cancer of the last several inches of the colon. Together, they’re often referred to as colorectal cancers.
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.
Signs and symptoms:
- A change in your bowel habits, including diarrhea or constipation or a change in the consistency of your stool
- Rectal bleeding or blood in your stool
- Persistent abdominal discomfort, such as cramps, gas or pain
- A feeling that your bowel doesn’t empty completely
- Weakness or fatigue
- Unexplained weight loss
- 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.
In most cases, it’s not clear what causes colon cancer. 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 aren’t needed. These cancer cells can invade and destroy normal tissue nearby. And cancerous cells can travel to other parts of the body.
Precancerous growths in the colon
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
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 don’t make cancer inevitable, but they can increase an individual’s risk of cancer significantly.
The most common forms of inherited colon cancer syndromes are:
- Familial adenomatous polyposis (FAP). 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 greatly increased risk of developing colon cancer before age 40.
- Hereditary nonpolyposis colorectal cancer (HNPCC). HNPCC, also called Lynch syndrome, increases the risk of colon cancer and other cancers. People with HNPCC tend to develop colon cancer before age 50.
FAP, HNPCC and other, rarer inherited colon cancer syndromes can be detected through genetic testing. If you’re concerned about your family’s history of colon cancer, talk to your doctor about whether your family history suggests you have a risk of these conditions.
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.
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’s likely that the cancer was completely removed, there may be no need for additional treatment.
Polyps that can’t 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.
Rectal cancer is the growth of abnormal cancerous cells in the lower part of the colon that connects the anus to the large bowel.
Rectal cancer develops usually over years; its actual cause is not known, but risk factors include increasing age (over 50), smoking, family history, high-fat diet, or a history of polyps or colorectal cancer or inflammatory bowel disease.
The major symptom of rectal cancer is bleeding from the rectum; other symptoms include anemia, fatigue, shortness of breath, dizziness and/or a fast heartbeat, bowel obstruction, small diameter stools, and weight loss.
For diagnosis, exams and tests may include fecal occult blood testing, endoscopy, digital rectal examination, sigmoidoscopy, CT/MRI imaging studies, along with routine blood tests and detection of carcinoembryonic antigen (CEA).
Medical treatment depends on the stage of rectal cancer (stages I-IV), with IV being the most severe stage; multiple chemotherapy medications are available and are chosen by the specialist (oncologist) to fit the individual’s stage of rectal cancer.
Surgery is used to both treat and reduce symptoms and, in some individuals, may result in a remission of the cancer. Radiation therapy is also used to kill or shrink rectal cancers. Follow-up is important to make sure that rectal cancer does not recur. Prevention involves detection and removal of precancerous growths.
The outlook or prognosis for individuals with rectal cancer is usually related to the stage of cancer, with stages III and IV having the poorest outcomes.