Background: Eri, although approved for advanced LPS, has limited activity in terms of tumor shrinkage. Anti-angiogenic agents have shown to increase tumor response in certain cancer types. This study aims to understand the safety, optimal dose, and efficacy of the combination of lenv, a multi-kinase anti-angiogenic inhibitor, and eri in LMS and LPS. Methods: Advanced LMS and LPS with no more than 2 lines of systemic chemotherapy were eligible. The starting dose was lenv 18mg/day daily and eri 1.1mg/m2 D1, D8 in a 21-day cycle. The primary endpoint of the phase Ib part was to assess the dose-limiting toxicity (DLT) in the first 21 days and to determine the recommended phase II dose (RP2D). A rule-based (≤ 33% DLT in first 6 pts) design was implemented in the phase Ib part. Results: From 2018 Jul 24 to 2019 Jan 8, a total of 6 pts (4 LMS, 1 dedifferentiated LPS, 1 myxoid LPS) were enrolled. The median age was 56 (range 30-70), female: male 3:3. Only 1 pt had a DLT, which was < 75% of the planned dosage. Within all (27) cycles, common grade (gr) 3 or higher adverse events (AE) included hypertension (HTN, n = 4), hand-foot syndrome (HFS, n = 3), and neutropenia (n = 4). However, 4 pts had late-onset gr3 or multiple coexisting gr2 AEs that necessitated dose reduction(s) (dr) for lenv (7 dr) or eri (2 dr) after the DLT assessment period (see table). The median time to 14 mg/day, 10mg/day of lenv, and eri 0.7mg/m2 was 22, 28 (after starting lenv 14mg/day), and 69 days, respectively. In terms of preliminary anti-tumor activity, 5 (83%) pts had target lesion shrinkage and 2 (33%) reached PR (1 confirmed) as best response according to RECIST 1.1. Conclusions: Late-onset AEs after cycle 1 leading to dose reduction was notable for lenv + eri and the RP2D was thus determined at a lower starting dose of lenv 14mg/day and eri 1.1mg/m2. The preliminary tumor response was also promising. Efficacy and safety of lenv + eri for LMS and LPS will continue to be explored in phase II study. Clinical trial information: NCT03526679