GT Biopharma shares surge 43.88% after hours as Phase 1 trial advances and IND submission for GTB-5550 nears.

GT Biopharma (NASDAQ: GTBP) surged 43.88% in after-hours trading following its third-quarter 2025 financial results and clinical updates. The company reported reduced R&D expenses ($0.6 million vs. $1.3 million in Q3 2024) and a $2.6 million cash balance sufficient to fund operations through Q1 2026. Key catalysts included advancements in its pipeline: the Phase 1 trial for GTB-3650 in hematologic malignancies advanced to Cohort 4 at 10 µg/kg/day, with the next update expected in Q1 2026, and an IND submission for GTB-5550 targeting B7H3-expressing solid tumors is anticipated by late December 2025 or January 2026. Management highlighted GTB-3650’s safety profile and competitive advantages over alternative therapies, while the IND timeline for GTB-5550 signaled regulatory progress. These developments, coupled with improved cost efficiency, drove optimism about the company’s near-term clinical and regulatory milestones.