Overview
Inhibrx Biosciences Inc shares rose 11.7% in pre-market trading on Monday after the company disclosed interim results from the Phase 2 portion of its HexAgon study. The data relate to INBRX-106, a hexavalent OX40 agonist, administered in combination with pembrolizumab and compared against pembrolizumab monotherapy in a first-line population.
Trial population and measured outcomes
The Phase 2 segment enrolled 68 patients overall. Randomization placed 33 patients in the INBRX-106 plus pembrolizumab arm and 35 patients in the pembrolizumab-only control arm. The evaluable cohort comprised 53 patients.
Within that evaluable population, 11 of 25 patients receiving the combination achieved a confirmed objective response, yielding a confirmed objective response rate (ORR) of 44.0% for the combination arm. By comparison, 6 of 28 patients in the control arm achieved a confirmed objective response, equivalent to a 21.4% ORR. The company reported this as a 22.6 percentage-point absolute increase in confirmed ORR for the combination versus pembrolizumab alone.
Three complete responses were documented in the combination arm; no complete responses occurred in the pembrolizumab monotherapy arm.
Mechanistic and safety findings
Peripheral blood analyses demonstrated mean increases in T-cell proliferation with the combination regimen. In patients treated with INBRX-106 plus pembrolizumab, mean proliferation of CD8+ and CD4+ T cells increased by up to 15-fold. By contrast, patients receiving pembrolizumab alone showed up to 2.5-fold mean increases. The company characterized these immune changes as providing mechanistic support for the clinical activity observed.
On safety, the combination displayed a manageable profile consistent with expectations for an immunotherapy combination. The most frequently reported treatment-related adverse events were rash, diarrhea, fatigue, and infusion-related reactions, with most events described as low-grade. No treatment-related deaths were reported in either arm of the Phase 2 portion.
Next steps and timing
Inhibrx indicated it expects progression-free survival data from the Phase 2 portion in the fourth quarter of 2026 and plans to initiate the Phase 3 portion during the third quarter of 2026.
Summary
The interim Phase 2 results show a higher confirmed objective response rate and evidence of amplified T-cell proliferation with INBRX-106 plus pembrolizumab versus pembrolizumab alone in first-line, treatment-naïve, PD-L1 positive metastatic or unresectable recurrent head and neck squamous cell carcinoma. The data coincided with an 11.7% pre-market increase in Inhibrx shares.