Cancer of the colon and rectum
Colorectal Cancer Update, 2008
by William Hocking, M.D
Colorectal cancer (CRC) occurs in the large bowel, approximately the last 120 centimeters or 5 feet of the intestinal tract. Cancers of the colon and rectum are the second leading cancer-related cause of death among men and women combined, after lung cancer.
In 2008 it is estimated there will be approximately 50,000 deaths from colon cancer in the United States, about 8-9% of all cancer deaths. The good news is that over the past decade, for the first time since data has been available, we are seeing a real decline in cancer death rates overall, and specifically in CRC where the death rate has declined about 26% from 1990 to 2004. This improvement can be attributed to a variety of factors including screening and early detection and more effective treatments. However, the number of people dying from CRC remains unacceptably high, particularly because it is a highly preventable disease with appropriate screening.
CRC usually begins in a colon polyp, an initially benign growth that may give rise to a cancer over several years. Prevention of colon cancer in part is aimed at detection and removal of polyps, which can then markedly reduce the chances of developing CRC (probably by 60-90%). This involves screening with a variety of methods. Testing the stool for occult blood on an annual basis has been proven to reduce mortality from CRC by helping to detect polyps or early cancers that can be treated effectively. Other screening methods include colonoscopy, flexible sigmoidoscopy, barium enema and most recently a new technique known as virtual colonoscopy (CT colography). Each of these approaches has advantages and disadvantages, but colonoscopy is widely considered the “gold standard.” In general, screening for an average risk individual should begin at age 50, but if there are known risk factors for CRC such as a family history of CRC or inflammatory bowel disease (ulcerative colitis or Crohn’s disease), it may be recommended that screening start 10 or more years earlier. There are two well-defined hereditary syndromes each with a very high risk of CRC: Familial Adenomatous Polyposis (FAP) and Hereditary Non-Polyposis Colorectal Cancer (HNPCC) or Lynch Syndrome. Other risk factors for CRC include age; high fat, low residue diet; smoking; excessive alcohol consumption. There is also some evidence that low doses of aspirin and calcium supplements may help reduce the risk of CRC.
Symptoms of CRC may not occur until the tumor has been present for some time. Symptoms may include blood in the stool, change in the size of the stool, constipation, diarrhea or abdominal pain. In some cases the initial symptoms may be due to anemia resulting from gradual blood loss, including chest pain or shortness of breath.
Once a diagnosis of CRC is made a staging evaluation should be done to determine the extent of the cancer and the best treatment options. In most cases, treatment will include removal of the involved section of colon or rectum. Today, the continuity of the bowel can usually be maintained and the need for colostomy is less frequent than in the past. Depending upon the stage of the disease at diagnosis and the estimated risk of recurrence, adjuvant chemotherapy may be recommended. This treatment usually lasts for about 6 months after surgery, and can substantially reduce the risk of cancer recurrence. Rectal cancer also often requires radiation therapy. In cases were the CRC has spread to another organ, surgery to remove the tumor may still be beneficial, but is sometimes done after initial treatment with chemotherapy. When the cancer is more extensive, surgery may not have a role, but chemotherapy is often helpful in prolonging life for several years. In the last decade many new chemotherapy drugs effective in treating CRC have been developed. Newer “targeted agents” that interfere with metabolic pathways in the cancer cell or prevent the growth of new blood vessels needed by the cancer have emerged and are having a major impact on the treatment of this disease.
These advances are the result of both basic research to better understand the disease process, and clinical trials to find more effective therapies. While treatment for CRC has markedly improved in the last decade, prevention of CRC by appropriate screening is by far the most effective strategy for preventing deaths and suffering from this disease. Every adult should discuss the best approach to screening with his or her physician.
William Hocking M.D.
Hematologist-Oncologist
Marshfield Clinic
