RG-7461

Purpose: This phase Ib trial evaluated fibroblast activation protein-α–targeted IL2 variant (FAP-IL2v), a novel immunocytokine engineered to minimize CD25-mediated toxicities, in combination with cetuximab, in patients with recurrent, unresectable, or metastatic head and neck squamous cell carcinoma (HNSCC).Patients and Methods: Patients received FAP-IL2v either on a continuous weekly (QW) schedule or QW for 4 weeks and then every 2 weeks (Q2W). Cetuximab was dosed at QW or Q2W schedules. The primary objectives were to evaluate the safety and tolerability, maximum tolerated dose, pharmacokinetics, and clinical activity for the combination of FAP-IL2v with cetuximab. Exploratory objectives included pharmacodynamic analyses.Results: A total of 58 patients were enrolled, 19 patients into the dose-escalation part, and 39 patients into the expansion part. The maximum tolerated dose of FAP-IL2v was defined as 10 mg (QW/Q2W) in combination with cetuximab (500 mg/m2, Q2W), which was further tested in the expansion part. The most common FAP-IL2v–related adverse events with a grade 3 or 4 severity were hypophosphatemia (19%), lymphopenia (16%), and infusion-related reaction (14%). The pharmacokinetics of FAP-IL2v in combination with cetuximab was similar to that after administration as monotherapy. Consistent with the proposed mode of action, FAP-IL2v preferentially expanded intratumoral NK and CD8 T cells. Four patients achieved a partial response, and the objective response rate was 7% (95% confidence interval, 3.2–14.7).Conclusions: The safety profile of FAP-IL2v in combination with cetuximab was acceptable, and pharmacodynamic markers support the proposed mode of action of this combination, but the overall low antitumor activity does not warrant further clinical exploration in HNSCC. [Part C of Study BP29842 (NCT02627274).]