Study demonstrates colonscopy is far less effective than previously believed

A Canadian study published in this month's Annals of Internal Medicine has profoundly altered our understanding of the effectiveness of colonoscopy as a screening device.  While doctors previously considered the colonscopy to be 90 percent effective in identifying tumors, results of this study suggest it is effective in preventing 60 to 70 percent of cancers.

The study appears to show that colonoscopy almost never identifies tumors in the right side of the colon where about forty percent occur.  It also failed to identify tumors on the left side of the colon one-third of the time.  Previous stuides have shown that it fails to identify a  particular type of flat or indented lesion in either location.

The American Cancer Society notes that the scope remains a valuable screening device, pointing out that mammograms prevent only 25 percent of breast cancer deaths, and PSA  tests have not been shown to affect the rate of prostate cancer deaths.  Experts note that the test had previously been "over-sold" and does not carry the "ten-year" reassurance that some doctors had previously ascribed to it. 

Experts  say this Canadian study points to the importance of thorough bowel-cleansing prior to the procedure and the importance of selecting a very careful physician to conduct it.  The procedure should be conducted as soon after bowel-cleansing as possible, and the physician conducting it needs to be deliberate and meticulous.  Good physicians should take more than eight minutes to inspect the colon and should maintain a high volume practice.  ("High volume" is defined as 3 to 4 tests per day on a regular basis:  apparently, as with most specialized procedures, there is a practice effect and specialists and practiced crews who conduct 200 or more procedures per year do a better job.)  Doctors carefully conducting testing should find polyps in one out of four men and in 15 percent of women screened.