More good news: some screening tests do seem to work

There’s a new manuscript in the NEJM saying that colonoscopies do prevent deaths from colon cancer:

BACKGROUND: In the National Polyp Study (NPS), colorectal cancer was prevented by colonoscopic removal of adenomatous polyps. We evaluated the long-term effect of colonoscopic polypectomy in a study on mortality from colorectal cancer.

METHODS: We included in this analysis all patients prospectively referred for initial colonoscopy (between 1980 and 1990) at NPS clinical centers who had polyps (adenomas and nonadenomas). The National Death Index was used to identify deaths and to determine the cause of death; follow-up time was as long as 23 years. Mortality from colorectal cancer among patients with adenomas removed was compared with the expected incidence-based mortality from colorectal cancer in the general population, as estimated from the Surveillance Epidemiology and End Results (SEER) Program, and with the observed mortality from colorectal cancer among patients with nonadenomatous polyps (internal control group).

What they found:

Of the more than 2600 patients in the study (who had polyps removed) only 12 had died of colorectal cancer a median of 15.8 years later. About 1250 had died of other causes. From known population data, we should have expected that more than 25 patients in this population should have died of colon cancer in this time. In other words, colonoscopy, with polyp removal, seems to have reduced mortality by more than 50%.

There are some cautions, however:

The type of evidence in this study, based on looking back at patient records, is not considered as reliable as that from a randomized controlled study, in which groups of patients are picked at random to have one treatment or another and then compared over time.

Dr. [Hal] Sox also said that because all of the patients in the study had adenomatous polyps, it is not certain that the findings would apply exactly to the general population, in which this type of polyp is found in about 15 percent of women and 25 percent of men.

In addition, Dr. Sox said, the people with polyps were part of a study that provided high-quality colonoscopy, so they may not have been comparable to the general population.

Other studies have found that doctors vary in their ability to find polyps, that certain types of polyps are hard to detect and that colonoscopy is better at finding polyps in the lower part of the intestine than in its upper reaches.

These types of studies are very expensive to do. Following patients for 20 years is hard and time intensive. Moreover, it would be almost unethical to do the randomized controlled trial now, as colonoscopy has become the standard of care. Nevertheless, data support the fact that colonscopy with polyp removal is associated with reduced mortality. Good news.

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