Background: MORAb-202 is an antibody drug conjugate consisting of farletuzumab (a humanized monoclonal antibody that binds to FRA) paired with a cathepsin B-cleavable linker to eribulin mesylate (a microtubule dynamics inhibitor). We report preliminary results from a FIH Ph1 study of MORAb-202 in pts with FRA-positive solid tumors. Methods: This open-label, ongoing, FIH study evaluated the safety, tolerability, pharmacokinetics, pharmacodynamics, maximum tolerated dose, and/or the recommended dose of MORAb-202 (Part 1: Dose finding part with accelerated modified toxicity probability interval design; Part 2: Expansion part). Eligible pts had FRA-positive solid tumors who failed standard therapy and an ECOG PS of ≤1. MORAb-202 was administered by intravenous injection once every 3 weeks and dose-limiting toxicities (DLTs) were assessed during the first 21-day cycle. Efficacy endpoints were assessed with RECIST v1.1 by investigator assessment. Results: As of Nov 16, 2018, 16 pts with confirmed FRA-positive tumors were enrolled and treated with MORAb-202 across 4 dose levels in Part 1 (0.3mg/kg: n = 3 [2 endometrial and 1 ovarian], 0.45mg/kg: n = 3 [3 ovarian], 0.68mg/kg: n = 3 [1 NSCLC, 1 ovarian, and 1 TNBC], 0.9mg/kg: n = 7 [4 ovarian, 1 endometrial, 1 NSCLC, and 1 TNBC]); all completed > 1 cycle. One pt in the 0.9mg/kg cohort experienced DLTs of alanine aminotransferase increased (grade 3) and gamma-glutamyl transferase increased (grade 3). Treatment-emergent adverse events (TEAEs) occurred in 15 pts (93.8%). The most common TEAEs were leukopenia and neutropenia (50% each). The objective response rate based on RECIST v1.1 was 37.5% (6/16 pts) in Part 1 with 1 complete response (ovarian) at 0.9mg/kg and 5 partial responses including 2 pts (both ovarian) at 0.9mg/kg, 1 pt (endometrial) at 0.3mg/kg, and 2 pts (1 TNBC and 1 NSCLC) at 0.68mg/kg. The disease control rate was 75% (12/16 pts). Exposure to MORAb-202 was dose proportional across the dose range investigated. Conclusions: MORAb-202 escalation to 0.9mg/kg was manageable with encouraging initial antitumor activity in pts with FRA-positive solid tumors. Clinical trial information: NCT03386942