A phase II clinical trial of neoadjuvant trabectedin in patients with nonmetastatic advanced myxoid/round cell liposarcoma (MRCL)

10525 Background: Trabectedin (ET-743, Yondelis), a marine-derived alkaloid has demonstrated significant activity in the treatment of soft tissue sarcomas (STS) in phase III trials, and has recently received EMEA approval in this indication. A subtype that accounts for 10% of STS, MRCL, displays the fusion FUS-CHOP in 95% of all cases. Preliminary results of neoadjuvant trabectedin (T) in advanced MRCL show reduction in the radiological density of the tumor, clinical improvement, and a pathological complete response (pCR) in the resected tumor mass. A phase II study to further determine the response to T in the MRCL population is presented. Methods: In this multicenter Phase II trial, patients (pts) with locally advanced (stage III) or locally recurrent MRCL were treated for 3 - 6 cycles with T (1.5 mg/m2 q3wk) in the neoadjuvant setting. Main endpoints were: pCR rate, objective response rate by RECIST, and correlation of molecular parameters from tissue samples with clinical outcomes. Results: Twenty-five pts with locally advanced MRCL have been recruited, of whom 20 are evaluable. All had the translocation (t12q13, 16p11) which causes the chimeric FUS-CHOP. Median age was 53 (23–75) and male:female ratio was 1. Thirteen pts completed therapy and underwent curative surgery. Pathological assessment was performed in 10 pts: 2 achieved pCR, 1 as per central pathology review and 1 by local pathology assessment. In addition, 1 pt had a very good pathological response. Ten patients remain to be histologically evaluated. Response rate by RECIST from pts who completed therapy was: 6 partial responses (46%) and 7 disease stabilizations. Remarkably, pathological response does not entirely correlate with response by RECIST since the pts with pCR still had radiological disease but no malignant component was found in the excised tumor mass (only connective and reactive tissue). Two serious adverse reactions of severe rhabdomyolysis, and asthenia, nausea and transaminase elevation were reported. Most common toxicities were liver enzyme elevation, neutropenia and thrombocytopenia. Conclusions: These preliminary results in terms of objective and complete pathologic responses, strongly suggest that T may have a role in the neoadjuvant setting in pts with MRCL. [Table: see text]