The purpose of this study is to test the study drug, BI 907828 for safety, effectiveness and side effects when compared to receiving the standard treatment, doxorubicin, in subjects with dedifferentiated liposarcoma (DDLPS). BI 907828 has proven to minimize a critical protein interaction between MDM2 and p53, two proteins in your body, which when their interaction is diminished, can stop the growth of your cancer. Patients with DDLPS are normally prescribed Doxorubicin as their standard treatment once they are diagnosed. The study also aims to find the recommended dose of the study drug, BI...