Phase 1 E303 Nectin-4–targeting antibody-drug conjugate in refractory solid tumors.

This first-in-human, open-label, multicenter Phase 1 study evaluates E303 (also referenced as SBE303), a Nectin-4–targeting antibody-drug conjugate (ADC) being developed by Samsung Bioepis. The trial uses sequential assignment with dose escalation and potential expansion to characterize safety/tolerability, dose-limiting toxicities, pharmacokinetics, immunogenicity, and early antitumor activity (including objective response rate by RECIST 1.1 with central review). Eligible patients have histologically confirmed, locally advanced unresectable or metastatic solid tumors that progressed after standard therapy, are intolerant of/decline standard therapy, or have no available standard option—so the population is “advanced refractory solid tumors” rather than a single tumor type. Scientifically, it targets Nectin-4, an adhesion protein expressed across multiple epithelial cancers; commercially, it represents Samsung Bioepis’s move beyond biosimilars into novel oncology drug development. Today’s care in this setting is tumor-specific and typically sequential systemic therapy (chemo, targeted therapy, and/or immunotherapy when indicated) plus best supportive care; this study tests whether Nectin-4–directed payload delivery can produce responses after standard options have failed.