Stomach cancer is the second leading cause of death from cancer worldwide. In Canada, there were 7 new patients/100,000 people in 2011. The 5-year survival is only 24%, making stomach cancer a leading cause of cancer-related death. Doctors caring for patients with stomach cancer make many treatment decisions, such as what chemotherapy (cancer fighting drugs) should be used, the best surgical approach (open or laparoscopic "key-hole" surgery), and if radiation might help. Although doctors make these recommendations based on the best evidence available, this evidence is incomplete since competing alternatives have not been directly compared to each other. Treatment costs and the quality of life for patients on these treatments also have not been studied. We will study 1300 patients in Ontario who received different treatments for stomach cancer to determine the results of these treatments (whether a patient's life was prolonged), treatment costs, and quality of life of the treated patients. Details about each patient and their cancer will have been gathered during a primary chart review, and will be linked to physician and hospital billing data. Treatment costs will be determined by interviews, review of published studies, and Ontario physician billing schedules. To get an idea of quality of life and out-of pocket costs, 140 patients will be given questionnaires. Cost, quality of life, and survival time will be combined to show the cost per life year gained by a treatment. The results of this study will help doctors decide which treatments achieve the best results. If two treatments have similar results, doctors could use the less expensive treatment. Doctors will also be interviewed to help determine what will help increase adoption of our recommendations. Our findings will be presented at international forums and will be published in a medical journal. We will also work with Cancer Care Ontario, to make sure doctors treating cancer patients have this information.