Colorectal cancer is the third most common non-skin cancer diagnosed in both men and women in the U.S. It is also the second leading cause of cancer deaths. Still, colorectal cancer is highly curable when it is detected early enough. Colorectal cancer, or "colon cancer" for short, is a result of cancer cells that form in the lining of the colon (large intestine) or rectum. Timely screenings can detect colon polyps, which are abnormal growths that sometimes become cancerous.
Colorectal cancer often begins as a benign growth known as a polyp. Adenomas are a type of polyp. These are benign tumors of the tissue lining the colon or rectum. Most polyps will stay benign, but some adenomas have the potential to turn into cancer over the long term. If they are removed early, this prevents them from turning into cancer.
Some risk factors for getting colorectal cancer are beyond your control. The following all increase the risk of getting colorectal cancer:
However, there are other risk factors for colorectal cancer that you can control. The following risk factors can be modified:
- Eating a diet high in red or processed meat, or eating meat cooked at high temperatures
- Overweight or obesity
- Inadequate exercise
- Cigarette smoking
- Drinking alcohol
Screening is important because colorectal cancer in its early stages usually doesn't produce any symptoms. Screening can detect the cancer before it produces symptoms, when it is most curable. After the disease begins to spread, it can produce blood in the stool, changes in bowel patterns (like diarrhea or constipation), abdominal pain, weight loss, or fatigue. Tumors that cause symptoms are typically larger and harder to treat.
It is recommended that most people have a colonoscopy screening every 10 years, starting at age 50. Some expert groups recommend starting at age 45. A colonoscopy allows examination of the entire colon and rectum using a tiny camera. This test can find cancers in the early, most treatable stage and actually prevent cancers from developing by removing polyps, as shown here.
An alternative to colonoscopy uses CT scan images to visualize the colon. This 10-minute to 15-minute procedure is known as a virtual colonoscopy. As with a conventional colonoscopy, the colon must be emptied as thoroughly as possible prior to the examination. In virtual colonoscopy, polyps or tumors are visualized without inserting the camera into the intestine. One disadvantage is that a virtual colonoscopy can only identify and not remove any polyps that are found. A standard colonoscopy is needed to remove polyps that may be identified.
An X-ray of the colon, known as a lower GI series, can provide another way to image the colon and rectum. A chalky liquid known as barium is used as a contrast agent and used as an enema. This photo shows an example of an "apple core" tumor that narrows the colon. As with a virtual colonoscopy, a real colonoscopy or other surgical procedure would be needed to remove any tumors or polyps that may be found.
If there are abnormalities seen in your colon or rectum, a biopsy is done to determine whether cancer is present. This can be done during a colonoscopy. The tissue is examined microscopically to look for cancer cells. This picture shows a highly magnified view of colon cancer cells.
Staging is the process of determining how far a tumor has spread beyond its original location. Staging may not be related to the size of the tumor. Treatment decisions also depend upon the stage of a tumor. Staging for colorectal cancer is as follows:
- Stage 0 – The cancer is found only in the innermost lining of the rectum or colon.
- Stage I – The cancer has not spread beyond the inner wall of the rectum or colon.
- Stage II – The cancer has spread into the muscle layer of the rectum or colon.
- Stage III – The cancer has spread to at least one lymph node in the area.
- Stage IV – The cancer has spread to distant sites in the body, such as the bones, liver, or lungs. This stage is NOT dependent on how far the tumor has penetrated or if the cancer has spread to lymph nodes near the tumor.
Higher stages mean that a cancer is more serious and has a worse prognosis. Patients with lower stages of colorectal cancer may have a 5-year relative survival rate of 91%, while that rate may drop to 14% for advanced-stage tumors.
Except for very advanced cases, colorectal cancer is usually treated by surgically removing the tumor and surrounding tissues. Surgery has a very high cure rate for early stage tumors. For advanced tumors that have spread outside the colon, surgery does not typically cure the condition, but removing larger tumors may reduce symptoms.
Colorectal cancer that has spread to the lymph nodes (stage III) can sometimes still be cured. In this case treatment usually consists of surgery and chemotherapy for colon cancer. In cases of rectal cancer, radiation therapy is added both prior to and following surgery in more advanced cases. Cancers that return after treatment or spread to other organs are harder to treat and more difficult to cure, but treatments may relieve symptoms and prolong life.
Modern chemotherapy drugs are less likely to cause nausea and other troubling side effects than older drugs, and medications are also available to help control these side effects. Clinical trials are always underway to develop better and more tolerable chemotherapy drugs.
Radiofrequency ablation (RFA) is a kind of cancer treatment that uses heat to destroy tumor tissue. CT scanning is used to guide insertion of a needle-like device into the tumor, through which intense heat is applied. RFA can be an option for destroying tumors that cannot be removed by surgery. In patients who have a few metastatic tumors in the liver that cannot be removed by surgery, chemotherapy is sometimes combined with RFA to destroy the tumors.
Eating a nutritious diet, getting enough exercise, and controlling body fat could prevent 45% of colorectal cancers, according to researchers. This means that adopting a healthy lifestyle can dramatically lower your risk of getting colorectal cancer. The National Cancer Institute recommends a diet low in fat with plenty of fiber and at least five servings of fruits and vegetables each day.
One study showed that people who got the most physical exercise were 24% less likely to get colorectal cancer than their least active counterparts. There was no difference if this activity was related to work or recreation. The American Cancer Society recommends at least 30 minutes of exercise a day for 5 or more days a week.
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