Inhibrx reports higher response rate with INBRX-106 combination in Phase 2 HexAgon study

Inhibrx Biosciences said September 8 that INBRX-106 plus pembrolizumab produced a confirmed objective response rate of 48.3%, compared with 26.5% for pembrolizumab alone, in the randomized, controlled Phase 2 portion of its HexAgon study. This is a primary endpoint results disclosure, not a regulatory approval or a completed registrational outcome.

Study population and response

The study evaluated the hexavalent OX40 agonist INBRX-106 in first-line, treatment-naive patients with PD-L1-positive disease, defined as CPS of at least 20, and metastatic or unresectable recurrent head and neck squamous cell carcinoma. Of 68 randomized patients, 63 were evaluable for the primary endpoint: 29 in the combination arm and 34 in the control arm. Four combination patients, or 13.8%, had complete responses, versus none in the control arm. The company said the study ran at more than 80 sites across the United States, Europe and Asia, with baseline prognostic factors largely balanced between arms.

Progression data remain interim

At the August 19 data cutoff, interim median progression-free survival was 9.6 months with the combination and 4.9 months with pembrolizumab alone. Six-month progression-free survival rates were 72.4% and 42.8%, respectively. These progression data continue to mature. In the HPV-positive subgroup, comprising 10 combination patients and nine control patients, confirmed response rates were 80.0% and 33.3%. Complete response rates were 30.0% and 0%, and six-month progression-free survival rates were 90.0% and 33.0%. Median progression-free survival had not been reached in the HPV-positive combination group, compared with 4.6 months in control. The small subgroup size limits how broadly those results can be interpreted.

Safety and next steps

Inhibrx described the combination's safety profile as generally manageable. The most common treatment-related adverse events were rash, fatigue and diarrhea, predominantly low grade. The company plans to add approximately 50 HPV-positive oropharyngeal squamous cell carcinoma patients with CPS of at least 1 to the randomized Phase 2 study to support a potential accelerated regulatory pathway. It then plans to seek alignment with the FDA and initiate Phase 3 HexAgon as an intended confirmatory study. Those are company plans; the disclosure does not establish FDA agreement or assure accelerated approval.

Filing context

The September 8 Form 8-K reports updated Phase 2 INBRX-106 data under Item 8.01. Item 7.01 furnishes the accompanying press release as Exhibit 99.1, with exhibits addressed under Item 9.01. The press release is furnished rather than filed for liability purposes under the filing's stated treatment.