The aim of this paper is to establish the patient flow diagram of a breast cancer center in a private hospital in Turkey and to decrease the current waiting time of patients by applying specific scenarios. With the help of the patient flow diagram and practices applied, the model is to increase the degree of welfare of patients and hospital personnel, to ensure that the resources are efficiently and effectively used, as well as minimizing the financial loss by decreasing the idle time spent in unnecessary queues. The patient flow diagram of the breast cancer center is modeled by means of commercial software ARENA. Discrete event simulations in ARENA are performed by using recorded data to find bottleneck of the system. Patients' queues are chosen as performance criteria. Various scenarios are derived to obtain a significant decrease of waiting time. The results showed that most of the performance criteria gave a significant difference compared to the actual situation whereas some of them are insignificant. Finally, the scenario, which gave the highest improvement, was chosen as the critical improvement scenario for the breast cancer center patient flow system. The increased demand versus insufficient sources caused in healthcare services due to poor quality with long queues during the diagnosis and treatment process, collection of data was the biggest challenge faced during observation. This model can only be used if adapted to processes of other cancer types, other breast cancer centers or any other unit in a hospital. This paper is giving an example of a current and future value stream map showing step by step where the bottlenecks are and how it can be improved and what specific benefits it will bring to the healthcare system specifically to breast center. It will be useful for both academicians and practitioners on how to apply lean to healthcare.