The participants of this study will have advanced epithelioid sarcoma. Sarcoma is a cancer of the connective tissues, such as nerves, muscles and bones. Epithelioid sarcoma is an ultra-rare sarcoma of the soft-tissue. Part 1 of this trial will study the safety and the level that adverse effects of each of the study drug combinations can be tolerated (known as tolerability). It is also designed to establish a recommended study drug dosage for the next part of the study. Part 2 will evaluate and compare for each of the study drug combinations how long participants live without their disease getting worse. The study drug is called tazemetostat. The study will test tazemetostat in combination with doxorubicin compared to placebo (dummy treatment) in combination with doxorubicin. Doxorubicin is a current front line treatment for epithelioid sarcoma.