Clinical studies are an essential step in the development of novel treatment methods for cancer and other diseases. They show researchers what works for the welfare of patients and what does not. In addition to safety and effectiveness they also determine whether the side effects of a new treatment are acceptable and, increasingly, what quality of life for patients is associated with a new therapy. Especially for rare cancers such as sarcomas, clinical studies are an important component of treatment concepts because here the standard forms of therapy are often limited. Nevertheless, only up to 5 % of cancer patients actually participate in clinical studies and a lot of studies have problems to recruit the necessary number of patients.