This is an open-label (patients will know the names of the study drugs they receive), randomized (patients will be assigned by chance to receive 1 of 2 treatment schedules with trabectidin) study designed to examine the the survival, safety, and pharmacokinetics (blood levels) trabectedin when administered to patients with 2 types of cancer (Liposarcoma or Leiomyosarcoma) who have received treatment with other anti-cancer therapy (Anthracycline and/or Ifosfamide). Trabectedin (also referred to as Yondelis) is a drug being developed to treat patients with cancer. Yondelis will be administered intravenously (i.v.) via a central catheter (tube) into a central vein once a week (0.58 mg/m2 as a 3-hour infusion on Days 1, 8, and 15 of each 28-day treatment cycle) or once every 3 weeks (1.5 mg/m2 administered as a 24-hour infusion on Day 1 of every 21-day treatment cycle) until disease progression. Patients in each arm will be pretreated with 20 mg of dexamethasone i.v. 30 minutes prior to each infusion.