Phase I-II prospective trial, multicenter, open label, exploring the combination of Trabectedin plus RAdiotherapy in Soft Tissue Sarcoma patients

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• Inclusion Criteria Cohort C and D 1. The patient must voluntarily sign the informed consent form before performing any study-specific test that is not part of the patient's usual care. 2. Aged between 18 and 75 years. 3. The following histological subtypes may be included in the cohort C: High grade leiomyosarcoma (G2-3), liposarcoma (G2-3), if at least 30% of the tumour is dedifferentiated, pleomorphic liposarcoma. The following histological subtypes may be included in the cohort D: Well differentiated liposarcoma (WD liposarcoma) and G2 dedifferentiated liposarcorcoma, if less than 30% of the tumour is dedifferentiated. A centralised diagnosis will be made to confirm that the patient can be included in the study. 4. The tumour must be located in the retroperitoneum and it must be resectable and without evidence of regional or distal spread after the appropriate staging process. This point must be confirmed by the central surgeon reviewer. 5. The location and size of the disease in the retroperitoneum must allow for compliance with radiotherapy limitations in healthy tissue. This point must be confirmed by the site's radiation oncologist and the central radiation oncologist reviewer. 6. Measurable disease according to CHOI criteria for cohort, and RECIST V 1.1 criteria for cohort D. 7. ECOG performance status 0–1. 8. Adequate haematological parameters (haemoglobin >10 g/dl, leukocytes ≥3,000/mm3, neutrophils ≥1,500/mm3, platelets ≥100,000/mm3). Patients with plasma creatinine ≤1.6 mg/dl, transaminases ≤2.5 times the ULN, total bilirubin ≤ ULN, CPK ≤2.5 times ULN, alkaline phosphatase ≤2.5 times ULN are acceptable. If the increase in alkaline phosphatase is >2.5 times the ULN, the liver fraction of alkaline phosphatase and/or GGT should be ≤ULN. 9. Fertile men or women must use an effective contraceptive method before starting the study, during the study and for 6 months following the conclusion thereof. Women of childbearing potential who participate in the study must undergo a pregnancy test before starting the study. 10. Normal cardiac function with LVEF ≥50% by echocardiogram or MUGA. 11. HBV and HCV serology must be performed before including the patient in the study. If HbsAg is positive, it is advisable to rule out a replicative phase (HbsAg*, DNA HBV+). If positive, the patient's inclusion in the trial is not recommended, and it is at the discretion of the investigator to administer preventive treatment with lamivudine. If a potential patient is positive to anti-HCV antibodies, the presence of the virus will be ruled out with a qualitative PCR, or the patient cannot be included in the study (if the qualitative PCR test cannot be performed on the patient, they cannot be included in the study). 12. Patient may have had one previous chemotherapy line (Only Cohort D). 13. The patient must have a central venous catheter for the administration of the treatment. -- For cohort A abd B please see the protocol--