Background: Cetuximab, an anti-EGFR mAb, is approved for R/M HNSCC but only a minority benefits. Activation of cMet, the receptor for hepatocyte growth factor (HGF), overcomes EGFR inhibition in preclinical models and high serum HGF is associated with resistance in patients (pts). We conducted a phase I trial evaluating the combination of cetuximab and ficlatuzumab, an IgG1 anti-HGF mAb, in pts with cetuximab-resistant, R/M HNSCC. Methods: In this Narayana k-in-a-row phase I design, cetuximab 500 mg/m² was administered every 2 weeks. Ficlatuzumab dose tiers were 10 mg/kg (tier 1) or 20 mg/kg IV every 2 weeks (tier 2), with inter-patient escalation or de-escalation based on cumulative dose-limiting toxicities (DLT). The recommended phase II dose (RP2D) was set at tier 2 if no DLTs were observed after 8 enrolled pts; expansion continued to n = 12. Key eligibility criteria: R/M HNSCC; recurrence within 6 months of cetuximab-radiation or progression during/within 6 months of palliative cetuximab; ECOG PS 0-1. Candidate biomarkers included serum Veristrat, a proteomic classifier in lung cancer where “good” predicts benefit from anti-EGFR therapy and “poor” indicates resistance and poor prognosis. Results: From Sept 2015–June 2016, 12 pts were enrolled and treated. Primary site: 1 oral cavity; 3 oropharynx (1 p16+); 2 hypopharynx; 5 larynx; 1 external auditory canal. Platinum-refractory: 11/12. Veristrat: 8 poor; 4 good. Three pts were treated at tier 1 and 9 at tier 2. No DLTs were observed. Grade 3 adverse events included: edema (1), hypoalbuminemia (1), infection (2), thromboembolic event (2). Median PFS and OS at RP2D were 6.0 mos (90% CI = 2.0 mos–not reached) and 8.2 mos (90% CI = 2.7 mos–not reached), respectively. Response rate was 17% (90% CI = 0–28%): 2/12 partial response (PR); 1/3 at 10 mg/kg; 1/9 at 20mg/kg. Clinical benefit rate (PR + stable disease) was 67%. Veristrat was not associated with PFS. Conclusions: The RP2D is cetuximab 500 mg/m² and ficlatuzumab 20 mg/kg every 2 weeks. This well-tolerated combination demonstrated promising activity in pts with poor prognosis, cetuximab-resistant R/M HNSCC. Phase II testing is justified. Clinical trial information: NCT02277197