Background: For advanced LPS and LMS, the two most common histologies in soft tissue sarcoma, there are limited treatment options that readily balance efficacy and toxicity. Patients (pts) treated with E had an improved median overall survival (OS) in a phase III randomized study compared to dacarbazine but with an unsatisfactory 4% objective response rate (ORR). Early studies of L, a multi-targeted anti-angiogenic inhibitor, had suggested efficacy in sarcoma pts. We hypothesized that the combination of anti-angiogenic agent and chemotherapy could potentiate treatment benefit and aimed to explore the safety and efficacy of L + E in advanced LMS and LPS. Methods: LEADER was a single-arm phase Ib/II study for advanced adult LMS and LPS pts who had received no more than 2 lines of systemic chemotherapy. The phase Ib part (starting dose: L 18mg/day, E 1.1mg/m²) had been reported and the recommended phase 2 dose (RP2D) was determined at L 14mg/day and E 1.1mg/m² D1, D8 every 21 days. The primary endpoint of the phase II part was ORR by RECIST 1.1, secondary endpoints included ORR by Choi criteria, progression-free survival (PFS), 6-month PFS rate, and OS. With α = 0.05 and 80% power, the pts needed for stage I and total of the Simon 2-stage design was 13 and 27 pts, respectively. Results: As of Jan 22, 2020, 20 pts (F/M 13/7) had been treated with at least one cycle of L + E; 14 were LMS (5 uterine, 9 non-uterine) and 6 were LPS (4 dedifferentiated, 2 myxoid round cell). The median age was 51 (range 29-73); the median lines of treatment(s) received before enrollment was 1 (range 0-3). 18 pts were evaluable for primary endpoint: the ORR by RECIST 1.1 was 27 % (5/18) (95% CI 10-53%). The ORR by Choi criteria was 67 % (12/18) (95% CI 41-87%). With 8 PFS events, the median PFS and 6-month PFS rate was 56 weeks (95% CI 25-not reached) and 72%, respectively. There were no OS events. The ORRs by RECIST 1.1 between different L starting doses were not significantly different (18mg 33% (2/6) vs 14mg 25% (3/12), p = 0.7). 15 pts experienced at-least one grade (gr) 3 or 4 adverse event (AE); gr 3 or 4 AEs occurred in > 1 pts included (% of phase Ib, % of phase II pts) hypertension (n = 4) (67%, 0%); hand-foot-syndrome (n = 4) (50%, 7%), proteinuria (n = 3) (0%, 25%), febrile neutropenia (n = 2) (17% vs 5%), neutropenia (n = 6) (50% vs 25%). The RP2D was associated with overall lower gr3/4 AEs except for proteinuria. Conclusions: L + E had shown promising efficacy in advanced LMS and LPS. L at 14mg/day had a better AE profile without compromising activity. The exploratory biomarker study of LEADER is ongoing. Clinical trial information: NCT03526679.