TRAbectedin in adVanced rEtroperitoneal well differentiated/dedifferentiated Liposarcoma and Leiomyosarcoma...

This is a multicentre, single-arm, phase II study aimed at further exploring the activity of trabectedin as second-/further-line treatment in retroperitoneal leiomyosarcoma (LMS) and well-differentiated/dedifferentiated liposarcoma (LPS).

The primary endpoint was the growth modulation index (GMI) defined as the ratio between PFS under trabectedin (PFS) and during previous chemotherapy treatment: time to progression (TTP-1). Secondary endpoints were objective response rate (ORR) and PFS. As per protocol, patients were considered responders if the GMI was >1.33, non-responders if <0.75 and neither if 0.76-1.32.

Overall 91 patients were assessable for the primary endpoint (32 patients with LMS and 59 patients with LPS): the median number of cycles received was 6.0 (Q1-Q3 3.0-12.0), and the main reason for treatment discontinuation was disease progression in 72% of patients. The median PFS was 6.0 months, while the median TTP1 was 7.5 months (8.1 and 6.4 months for LMS and LPS, respectively). Thirty-three patients [52%, 95% confidence interval (CI) 36% to 58%, P = 0.674, odds of response 1.1] had a GMI >1.33 (LMS 46%, 95% CI 26% to 67%, odds of response 0.85; LPS 56%, 95% CI 40% to 72%, odds of response 1.3). Overall, in LPS we observed 15/47 patients with a GMI <0.5 and 15/47 patients with a GMI >2. Among LMS patients, 9/26 had a GMI <0.5 and 10/26 had a GMI >2. Overall, ORR (complete response + partial response) was 16% (24% for LMS and 12% for LPS).

While the primary endpoint of the study was not met, we noticed a subgroup of patients with a markedly discrepant TTP with trabectedin in comparison to previous therapy (GMI <0.5 or >2, the latter including some patients with a long TTP with trabectedin). A mismatch between PFS and overall survival was observed, possibly due to the natural history of the two different histologies and the availability of further lines in LMS.