Trabectedin (T) in desmoplastic small round cell tumor (DSRCT): Report of its effect in 3 relapsed patients (pts) and the comparison of different regimens in a patient-derived xenograft (PDX) model.

Abstract

e23553 Background: DSRCT is an ultra-rare soft tissue sarcoma marked by the presence of the EWS-WT1 translocation and a dismal prognosis. Anecdotal activity of T in DSRCT pts was reported. We describe herein three advanced DSRCT pts treated with T and a comparative assessment of doxorubicin (D), pazopanib (P) and T in a patient-derived xenograft (PDX) model of DSRCT. Methods: Three pts (#1, #2 and #3) suffering from progressive, metastatic, unresectable relapsing disease from a primary peritoneal DSRCT previously treated with 8 cycles of anthracycline-based neoadjuvant chemo and complete surgical resection, were started on T (1.3 mcg/sqm every 3-4 weeks). A PDX model was generated by subcutaneously implanting small tumor fragments obtained at surgery from a treatment-naïve DSRCT patient into the right flank of SCID mice. Consistency of PDX and the originating tumor was confirmed in terms of histomorphology and presence of the EWS-WT1 gene fusion. Mice were randomized to receive D, P and T, administered as single agents at optimal doses and schedules. Drug activity was assessed in terms of tumor volume inhibition (TVI) percentage in treated versus control mice. An orthotopic xenograft model was also generated by injecting DSRCT cells into the peritoneal cavity of SCID mice. Results: At the time of this report, pt #1 and #2 are on therapy with T, with a partial response by RECIST maintained after 48 and 36 months from treatment start, respectively, while #3 progressed after 4 months. In the DSRCT PDX model, T was the most effective drug, with a maximum TVI of 82%, while D and P showed lower, comparable activity (maximum TVI: 59% and 66%, respectively). In the orthotopic DSRCT PDX, DSRCT cells spreading in the abdominal cavity generated different tumor masses, properly recapitulating the dissemination pattern in patients, confirming the reliability of this preclinical model. Conclusions: Both our preliminary model and our further clinical observations support the potential of T in DSRCT. A confirmatory prospective clinical study is now warranted.