A Comparison of Screening Methods for Colorectal Cancer

Abstract

Colorectal cancer (CRC) is the second leading cause of cancer death in the United States. This cancer has a very long asymptomatic phase and most patients are not aware of its presence until it grows into an advanced stage when the survival chance is very low. Evidence from several studies suggests that screening for detecting and removing colorectal cancer and precancerous adenomatous polyps can reduce the incidence of CRC and colorectal cancer-related mortality. There are a number of screening methods designed for this purpose, which vary considerably in terms of their performance characteristics and cost. However, because of the long latency of CRC and time needed for clinical trials, it is not practical to provide clinical trials of all the screening strategies for CRC. Simulation models offer an alternative means to evaluate and compare screening strategies.

The primary goal of this thesis was to add a screening structure onto an existing discrete-event simulation model of the natural history of the CRC. The enhanced model is capable of simulating various screening interventions. It is the only model that can simulate all the screening strategies recommended by the American Gastroenterological Association clinical guidelines.

In order to compare the screening strategies in these guidelines, a deterministic cost-effectiveness analysis (CEA) was first performed. CEA is considered the most appropriate method of evaluating preventive health services from an economic perspective. The model provides the discounted cost and effectiveness of each of the screening strategies which are the key inputs for CEA.

Adopting a Bayesian approach, an appropriate distribution was assigned to strategic and economic parameters of the model to compare the screening strategies under the uncertainty. A probabilistic sensitivity analysis was performed for this purpose and the empirical distributions for average cost-effectiveness (CE) ratio of screening methods along with their 95% confidence intervals were developed on the CE plane.

Finally, the cost-effectiveness acceptability curves (CEAC) were derived from the CE planes. These curves present the probability that a screening strategy is cost-effective for different ceiling ratios, which is the money society is willing to pay to gain a year of life. Examining the CEAC for all the populations (average and high risk), fecal occult blood test (FOBT), combined sigmoidoscopy & FOBT, and colonoscopy were three screening strategies showing higher probabilities to be the most cost-effective strategy for different ceiling ratios. In general, CEAC provide a probabilistic comparison between screening strategies, which can be used by medical policy makers for guideline development and health-care resource allocation. This thesis is the first effort to compare multiple number of CRC screening strategies by using CEAC.