COST-EFFECTIVENESS OF COLORECTAL CANCER SCREENING IN ARAGON (SPAIN)

Purpose: To evaluate the cost-effectiveness of a screening program for colorectal cancer CRC. Method(s): We built a state-transition model encoded as a Markov influence diagram (MID) and implemented it with the open-source software tool OpenMarkov. The screening instrument is the immunochemical fecal occult blood test (IFOBT) with the cut-off point at 117 ng/mL, performed every two years. The variable State has nine states: normal epithelium, small adenoma, large adenoma, CRC, follow-up after low-risk adenoma, follow-up after high-risk adenoma, and dead. The variable CRC Stage has five states: stages I to IV and "none". A colonoscopy is performed when the test is positive and also when the patient has symptoms of CRC. The probabilities and the quality of life values were obtained from the literature; the uncertainty about them was modeled with Beta and Dirichlet distributions. Costs are those of the health system of Aragon, a region in the in northeastern Spain; each cost was assigned a Gamma distribution with a standard deviation of 10%.

The evaluation of the model departed from a cohort of 30-year-old individuals with normal epithelium and no adenomas or cancer, and ended at the age of 100. The screening program was assumed to start when the individuals reach the age 50 or 60 and to end when they are 69. We did not evaluate the model for earlier starting ages because of the lack of reliable incidence data for younger populations. We also performed a probabilistic sensitivity analysis with 1,000 simulations. In all the analyses we discounted costs and effects at 3% p.a. Result(s): The incremental cost-effectiveness ratio (ICER) was 1,055 €/QALY when the screening starts at the age of 50, and 947 €/QALY when it starts at the age of 60. These ratios are significantly lower than those obtained in previous studies. The sensitivity analysis concluded that, for a willingness to pay of 30,000 €/AVAC (the value usually accepted as the shadow threshold for the public health system in Spain) CRC screening is cost-effective with a probability of 100%. Conclusion(s): According to our model, CRC screening with the immunochemical fecal occult blood test applied biennially is highly cost-effective for individuals between 50 and 69 years old.