Study of RiMO-301 and Radiotherapy With PD-1 Inhibitor for the Treatment of Head-Neck Cancer

Primary Objectives: * To determine the tolerability of RiMO-301 with hypofractionated X-ray radiotherapy and a PD-1 inhibitor (pembrolizumab or nivolumab) in patients with unresectable, recurrent or metastatic head-neck cancer * To determine the efficacy of RiMO-301 with hypofractionated X-ray radiotherapy and a PD-1 inhibitor (pembrolizumab or nivolumab) Secondary Objectives: * To evaluate progression-free survival for up to 12 months * To determine overall survival for up to 24 months * To assess patient quality of life The target population is patients with unresectable, recurrent or metastatic head-neck cancer which is clinically accessible to intratumoral injection.