Randomized controlled, open-label, phase IIb/III study of lurbinectedin in combination with doxorubicin versus doxorubicin alone as first-line treatment in patients with metastatic leiomyosarcoma.

TPS11590 Background: Lurbinectedin (LUR) is a synthetic chemical entity structurally related to trabectedin that inhibits oncogenic transcription and is active in tumors addicted to transcription. Synergistic activity of the combination of LUR with Doxorubicin (DOX) was found in solid tumors. Preliminary results from two trials showed efficacy for LUR/DOX in anthracycline-naïve advanced Leiomyosarcoma (LMS) (1 st or 2 nd line) at different doses. In a phase 2 trial in soft tissue sarcoma (STS) patients (pts) (mostly with LMS: 12/20 pts), a combination of DOX 50 mg/m 2 + LUR 2 mg/m 2 Day (D)1 q3wk resulted in a response rate (RR) of 35% (4/7 LMS pts responding) and a disease control rate (DCR) at 24 wks of 40% (1). A phase 1b/2 trial in 10 advanced STS pts found a RR of 60% (5 were LMS, with 3 partial responses) treated at DOX 25 mg/m 2 D1 or D1,D8 + LUR 3.2 mg/m 2 D1 q3wk, (2). The promising results of these trials provide a rationale for further exploring this combination in a phase 2b/3 trial as first-line therapy for metastatic LMS (SaLuDo - NCT06088290). Methods: SaLuDo is a randomized, open-label study evaluating LUR in combination with DOX compared to DOX alone as first-line treatment of pts with metastatic LMS. The primary endpoint is progression-free survival (PFS) according to Independent Radiological committee (IRC). Secondary endpoints include overall survival, PFS according to Investigator assessment (IA), overall response rate, duration of response, and clinical benefit rate (according to IRC and IA), safety profile, patient-reported outcomes, pharmacokinetics, and exploratory pharmacogenomic analysis. Main inclusion criteria include age ≥ 18 years, confirmed diagnosis of metastatic LMS, and no prior systemic treatment for metastatic disease. Exclusion criteria include prior treatment with anthracyclines, lurbinectedin or trabectedin. The phase 2b part of the study will randomize approximately 120 pts into 3 arms (1:1:1): Control arm (DOX 75 mg/m 2 D1 q3wk; experimental ARM A (DOX 50 mg/m 2 D1 + LUR 2.2 mg/m 2 D1 + 1ry GCSF prophylaxis q3wk), and experimental ARM B (DOX 25 mg/m 2 D1 + LUR 3.2mg/m 2 D1 + 1ry GCSF prophylaxis q3wk). Stratification will be done according to site of primary tumor (uterine vs. soft tissue), sites of metastatic disease (lung as unique site vs. other) and time from diagnosis to study entry (≤ 12 months vs. >12 months). One of the two experimental arms will be dropped out at the end of phase 2b. The study will then enter the phase 3 part and approximately 120 pts will be randomized 1:1 between the control arm and the selected experimental arm. An Independent Data Monitoring Committee will oversee the conduct of the study. The first patient was randomized in 09/2023. The phase 2b part of the study is ongoing and recruiting patients in Europe and the USA. 1. Cote EJC 2020; 126:21-32. 2. Cote. JCO 2023; 41: Abst 11507. Clinical trial information: NCT06088290 .