Regeneron Pharmaceuticals is trading 13.04% down at $659.42 after-hours. - Rival Kodiak Sciences reported positive Phase 3 DAYBREAK results for its eye-drug candidates, Zenkuda and tabirafusp-ted, on September 28, demonstrating non-inferior vision gains compared to Regeneron's Eylea. - This development creates competitive pressure on Regeneron's lucrative eye-drug franchise, which market observers linked to the decline in REGN's stock. - REGN closed September 30 at $758.27.