The purpose of this study is to evaluate the safety and efficacy of trabectedin for the treatment of localized (non-metastatic) myxoid / round cell liposarcoma (malignant tumor derived from primitive or embryonal lipoblastic cells).

This is an open-label (all people know the identity of the intervention), prospective (study following participants forward in time), multicenter (when more than one hospital or medical school team work on a medical research study) study of trabectedin for the treatment of localized myxoid / round cell liposarcoma (MRCL). Trabectedin will be given at 1.5 milligram per meter square (mg/m^2) over a 24-hour intravenous (iv) infusion every 3 weeks for a minimum of 3 and a maximum of 6 cycles along with dexamethasone 20 mg iv which will be given within 30 minutes before start of each trabectedin iv infusion. Participants whose myxoid/round cell liposarcoma (MRCL) do not progress at the end of the neoadjuvant treatment will be followed every 6 weeks for disease progression or until 6 months post definitive surgery, in the absence of unacceptable toxicity and/or disease progression. Efficacy will be assessed by determining the pathologic Complete Response (pCR) rate assessed in the tumor surgical specimen by a central pathology review. Participants' safety will be monitored throughout the trial.

Inclusion Criteria:

• Pathological diagnosis of myxoid / round cell liposarcoma (MRCL) and availability of pathology specimens for central review and pharmacogenomic studies
• Clinical evidence of locally advanced (Stage III), non-metastatic tumor, including locally recurring disease after initial surgery
• Measurable disease (by Response Evaluation Criteria In Solid Tumors [RECIST])
• No prior chemotherapy or radiation (except for adjuvant post-operative radiotherapy)
• Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) 0-2

Exclusion Criteria:

• Known hypersensitivity to any of the components of the trabectedin intravenous (iv) formulation or dexamethasone
• Pregnant or lactating women and women of reproductive potential who are not using effective contraceptive methods
• History of another neoplastic disease (except basal cell carcinoma or cervical carcinoma in situ adequately treated) unless in remission for 5 years or longer
• Known distant metastases
• Other serious illnesses such as congestive heart failure or angina pectoris, myocardial infarction within 1 year before enrollment, uncontrolled arterial hypertension or arrhythmias