How colorectal cancer is diagnosed

Fecal occult blood testing, barium enema, sigmoidoscopy, and colonoscopy are used to diagnose colorectal cancer. Because colorectal cancer can cause intestinal bleeding, a blood test is used to check for anemia (a low red blood cell count).

Imaging tests such as ultrasound, CT scans, MRI, chest x-rays, and angiography (an x-ray technique that uses an injected contrast material) may be used to visualize the intestines or to see if the cancer has spread to other sites in the body.

If cancer is diagnosed, the stage of the cancer must be identified to determine the best course of treatment. The stage of the cancer is based on how large the tumor is and whether it has spread to the lymph nodes or other parts of the body.

Treatment of colorectal cancer

Surgery is the most common treatment for colorectal cancer and can eliminate the cancer in about half of all cases. It involves removing part of the colon or rectum that contains the cancer, some of the healthy tissue that surrounds it, and nearby lymph nodes (to determine if the cancer has spread to the lymphatic system).

Common side effects of surgery include diarrhea or constipation, which usually improves on its own.

Other treatments for colorectal cancer include chemotherapy and radiation therapy, which can be used alone, in combination, or with surgery. Chemotherapy delivers medication intravenously to attack cancer cells throughout the body. It can be used after surgery (to increase the odds that all cancer cells have been eliminated) or before surgery to help shrink a tumor.

If colorectal cancer has spread, chemotherapy may be used to slow the progression of the cancer and relieve symptoms (without the expectation of a cure). Adverse effects may include

  • nausea
  • vomiting
  • fatigue
  • diarrhea
  • mouth sores
  • hair loss
  • bone marrow suppression

Radiation therapy involves directing x-rays at the cancer cells. It is used only for rectal cancer. Unlike chemotherapy, which affects the whole body, radiation therapy specifically targets cancer cells while minimizing damage to healthy cells. As with chemotherapy, it may be used before or after surgery, or for symptom relief when cancer has spread and a cure is not possible.

The radiation may be delivered internally from implanted radioactive "seeds" or externally from an x-ray machine. Common adverse events include

  • fatigue
  • nausea
  • diarrhea
  • appetite loss
  • bloody stool
  • damage to the skin and other organs near the radiation site

Publication Review By: H. Franklin Herlong, M.D.

Published: 28 Mar 2011

Last Modified: 08 Sep 2015