Nowadays Brazil has a complex cancer care scenario. There are nearly 600.000 new cancer cases each year in Brazil, and the huge majority of patients have some contact with hospital services. However, long waiting queues for diagnostics and treatments have become common. One of the critical success factors in a cancer treatment is early diagnosis. The reduction of waiting time to start therapeutic procedures is one of the main issues for improvement of patient's quality of life and possibilities of cure. The objective of this work is to describe the development of a decision support system that improves the identification of access alternatives, appointment scheduling and employment of available resources. The Theory of Constraints was used to identify bottlenecks in patient treatment flow and a Discrete Events Simulation model was used to reduce patients' waiting time to start cancer treatment.