In an average-risk population, screening colonoscopies yield different incidences of colorectal cancer and different cancer-related mortality, depending on the operators’ adenoma detection rates, according to a report published online June 16 in JAMA.

Adenoma detection rates vary dramatically among gastroenterologists, and patients of physicians who have lower ADRs are known to have higher rates of both colorectal cancer and fatal colorectal cancer. But little is known about the effect different ADRs have on the lifetime benefits and risks of colonoscopy screening programs on average-risk populations. It is possible that the harms of high ADRs outweigh the benefits. For example, higher ADRs may signal increased detection of small low-risk polyps, leading to more surveillance colonoscopies as well as more complications – all from lesions that may well have been benign, said Reinier G.S. Meester of the department of public health, Erasmus University Medical Center, Rotterdam (the Netherlands), and his associates.

They examined various possible outcomes for a colonoscopy screening program at different levels of adenoma detection using microsimulation modeling that incorporated data from a large U.S. HMO concerning 57,588 screening colonoscopies performed by 136 physicians between 1998 and 2010. Adenoma detection rates – the percentage of a physician’s screening colonoscopies that detected at least one histologically confirmed adenoma – ranged from 7.35% to 52.51%. The investigators categorized the data into five equal subsets according to the physicians’ ADRs; the first quintile had a mean ADR of 15.32%; the second quintile, 21.27%; the third quintile, 25.61%; the fourth quintile, 30.89%; and the fifth quintile, 38.66%.

The simulation cohort comprised 10 million men and women, and the investigators performed 1,000 simulation runs, varying 13 relevant parameters with each run. They found that patients of physicians in the first quintile had a lifetime risk of colorectal cancer of 26.6 per 1,000; this decreased in a linear fashion with each quintile, so that patients of physicians in the fifth quintile had a lifetime risk of colorectal cancer of 12.5 per 1,000. Lifetime risks of colorectal cancer death followed the same pattern, decreasing from 5.7 per 1,000 in the first quintile to 2.3 per 1,000 in the fifth quintile.

The simulated lifetime risk of colorectal cancer dropped an average of 11% with every 5% increase in ADR, and the simulated lifetime risk of colorectal cancer death dropped an average of 13% with every 5% increase in ADR. This translates to a 50%-60% lower incidence of colorectal cancer and 50%-60% lower cancer-related mortality for patients of physicians with the highest ADRs, compared with physicians with the lowest ADRs, wrote Mr. Meester and his associates (JAMA 2015 June 16 [doi: 10.1001/jama.2015.6251 ]).