Title: Gastric cancer prevention policy
Description: Gastric cancer is the second leading cause of cancer-related deaths, with over 65% of all cases occurring in developing countries. Helicobacter pylori (Hp) infection is the most important risk factor for gastric cancer and estimated to be responsible for 65 to 80% of all cases. Clinical trials suggest Hp treatment reduces disease progression, but the effectiveness of treatment to reduce long term outcomes, such as gastric cancer mortality, is uncertain. To assess the economic and population impacts of Hp screening, we developed a comprehensive simulation model of gastric cancer. In Chapter 1, we describe the development and calibration of a natural history model of gastric cancer in the two high-risk countries of China and Colombia. Using a likelihood-based calibration approach, we identified multiple parameter sets that provided model outcomes consistent with epidemiological data on the prevalence of precancerous lesions and gastric cancer incidence in each country. The model is capable of evaluating the relative effectiveness of primary and secondary prevention efforts and reflecting the uncertainty surrounding disease progression on important policy outcomes. In Chapter 2, we use the model to estimate the health and economic consequences associated with Hp screening in China, where over 40% of the world's gastric cancer cases occur. We estimated that a once per lifetime screening program for 20-year olds may prevent as many as one in every four to six cancers and appears to be highly cost-effective given commonly used threshold heuristics. Given the ease of detecting and treating Hp infection and the poor prognosis and limited treatment options for gastric cancer, adopting a more proactive strategy may be reasonable while awaiting additional clinical trial evidence on the benefits of Hp treatment.

In Chapter 3, we develop a population model of gastric cancer among men in China to better understand the population level dynamics of the disease and changing risk factor trends. We found that gastric cancer rates have declined as Hp prevalence has fallen, despite the rise in smoking. Even with the continued decline of Hp and smoking, we estimated that the number of new gastric cancers in 2030 will rise substantially as a result of population growth and aging. While targeted Hp reduction programs may prevent a proportion of these cancers, their impact on population gastric cancer risk will not be realized for several decades and finding effective strategies for primary or secondary prevention of gastric cancer should be a public health priority.