Colorectal Cancer Screening and Prevention Technique (page 2 of 4)

Chemoprevention
Another exciting area in colon and rectal cancer is the concept of chemoprevention. This essentially asks the question: “Is there a medication or vitamin my patients can take that will reduce their risk of developing colon cancer?” There are many reports in the lay press and in the medical literature suggesting that some agents may be beneficial in preventing or reducing polyps in at-risk patients. Agents that have been studied include NSAIDS such as sulindac and celecoxib, aspirin, calcium and fiber.

The protective effect of NSAIDS is thought to be secondary to decreasing the expression of the
cyclooxygenase (COX)-2 enzyme within the colonic mucosa. There are two isoforms of the COX enzyme that have been studied. The COX-1 enzyme is universally expressed in all tissues and is not increased in inflammatory or cancer conditions.
COX-2 expression has been found to be increased in tumor cells for lung, breast, colon and several other cancers. Increased expression of COX-2 enzyme leads to increased levels of prostaglandins in these tissues. Prostaglandins have effects on mitogenesis, cellular adhesion, immune surveillance, angiogenesis and apoptosis. Aberrations in these cellular functions can lead to the development of malignant cells and cancer. Decreasing prostaglandins by inhibiting the COX-2 enzyme appears to have a protective effect against polyp development and progression to cancer.

Historically, NSAIDS were first studied in conjunction with FAP. A common operation in the past for FAP was a total abdominal colectomy with ileal rectal anastomosis. Because the rectum is left in place, these patients are then followed with serial proctoscopy and polypectomy when indicated. In one such patient who was being treated with sulindac for a non-gastrointestinal problem, it was noted that fewer and smaller polyps were found than before the initiation of sulindac therapy. Subsequent studies found that treatment with sulindac resulted in a decrease in the number of polyps found on colonoscopy in patients with FAP who had not undergone colectomy.

One must be cautious when counseling patients with FAP regarding the use of these agents. Sulindac and celecoxib have been shown to decrease the number of polyps by as much as 28-50 percent. This, however, does not cure FAP or stop the progression of the disease. It also does not change the genetic mutation that causes FAP, the adenomatous polyposis coli (APC) gene. While these medicines can decrease the need for polypectomy and facilitate surveillance of the colon, it does not obviate the need for colectomy to prevent the development of colon cancer. It may be beneficial in patients with an ileal rectal anastomosis so as to decrease the number of polyps in the rectum, making surveillance polypectomy easier. Patients must also be aware that rectal cancers have been reported in patients who have been treated with these medications.