Variation in Adenoma Detection Rate and the Lifetime Benefits and Cost of Colorectal Cancer Screening: A Microsimulation Model

Abstract

Importance: Colonoscopy is the most commonly used colorectal cancer screening test in the United States. Its quality, as measured by adenoma detection rates (ADRs), varies widely among physicians, with unknown consequences for the cost and benefits of screening programs.

Objective: To estimate the lifetime benefits, complications, and costs of an initial colonoscopy screening program at different levels of adenoma detection.

Design, setting, and participants: Microsimulation modeling with data from a community-based health care system on ADR variation and cancer risk among 57,588 patients examined by 136 physicians from 1998 through 2010.

Exposures: Using modeling, no screening was compared with screening initiation with colonoscopy according to ADR quintiles (averages 15.3%, quintile 1; 21.3%, quintile 2; 25.6%, quintile 3; 30.9%, quintile 4; and 38.7%, quintile 5) at ages 50, 60, and 70 years with appropriate surveillance of patients with adenoma.

Main outcomes and measures: Estimated lifetime colorectal cancer incidence and mortality, number of colonoscopies, complications, and costs per 1000 patients, all discounted at 3% per year and including 95% confidence intervals from multiway probabilistic sensitivity analysis.

Results: In simulation modeling, among unscreened patients the lifetime risk of colorectal cancer incidence was 34.2 per 1000 (95% CI, 25.9-43.6) and risk of mortality was 13.4 per 1000 (95% CI, 10.0-17.6). Among screened patients, simulated lifetime incidence decreased with lower to higher ADRs (26.6; 95% CI, 20.0-34.3 for quintile 1 vs 12.5; 95% CI, 9.3-16.5 for quintile 5) as did mortality (5.7; 95% CI, 4.2-7.7 for quintile 1 vs 2.3; 95% CI, 1.7-3.1 for quintile 5). Compared with quintile 1, simulated lifetime incidence was on average 11.4% (95% CI, 10.3%-11.9%) lower for every 5 percentage-point increase of ADRs and for mortality, 12.8% (95% CI, 11.1%-13.7%) lower. Complications increased from 6.0 (95% CI, 4.0-8.5) of 2777 colonoscopies (95% CI, 2626-2943) in quintile 1 to 8.9 (95% CI, 6.1-12.0) complications of 3376 (95% CI, 3081-3681) colonoscopies in quintile 5. Estimated net screening costs were lower from quintile 1 (US $2.1 million, 95% CI, $1.8-$2.4 million) to quintile 5 (US $1.8 million, 95% CI, $1.3-$2.3 million) due to averted cancer treatment costs. Results were stable across sensitivity analyses.

Conclusions and relevance: In this microsimulation modeling study, higher adenoma detection rates in screening colonoscopy were associated with lower lifetime risks of colorectal cancer and colorectal cancer mortality without being associated with higher overall costs. Future research is needed to assess whether increasing adenoma detection would be associated with improved patient outcomes.

Figure 1. Sensitivity analysis results: The adenoma detection rate-outcome relationship for various modeling scenarios.^a

Abbreviations: ADR = adenoma detection rate; attr. = attributed. ^a95% confidence intervals were relatively narrow because we applied the same assumptions for the natural history of colorectal cancer to all patients (Table 1). Colonoscopy sensitivity was the only assumption varied independently for each ADR quintile. ^bResults were similar for years of life lost to cancer. ^cWe evaluated four alternative causal models for the observed cancer incidence differences across the ADR quintiles: in scenario 2 all variation in ADR was attributed to sensitivity of colonoscopy for small adenomas under 5 mm, which varied from 5.4 in the lowest quintile to 98% in the highest quintile; in scenario 3 all ADR variation was attributed equally to sensitivity for small, medium and large adenomas, which varied from 26.0 to 98%; in scenario 4 it was assumed that the rate of completeness of colonoscopy along with differences in colonoscopy sensitivity accounted for the observed ADR-variations, varying from 75% to 98%; in scenario 4 adenoma prevalence was assumed to be up to a relative 25% higher with higher ADR. ^dUnder intensified surveillance, we assumed that all patients with adenomas detected at colonoscopy underwent surveillance at 3 years after the procedure, and patients with a negative surveillance colonoscopy underwent surveillance at 5 years. For reference, in the base-case analysis, patients with adenomas detected at colonoscopy were referred for surveillance after 3 or 5 years, depending on the number and size of the adenomas detected. Likewise, patients with a negative surveillance colonoscopy were referred for a follow-up colonoscopy in 5 or 10 years, depending on whether the preceding interval was 3 or 5 years. ^e95% confidence intervals were derived by multiway probabilistic sensitivity analysis. ^fThe mean differences in simulated outcomes per 5 percentage-point higher ADR were derived by linear regression, and presented relative to the model outcomes for ADR quintile 1 (formula: 5 × beta_ols/outcome_q1).