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

Inclusion Criteria: * Diagnosis of head-neck cancer that requires palliative radiotherapy * Patients with unresectable, recurrent or metastatic HNSCC, regardless if the patients have progressed on or are intolerant to platinum-based chemotherapy prior to study enrollment or if the patients are receiving pembrolizumab in the first line: * receiving a PD-1 inhibitor (pembrolizumab or nivolumab) as a standard of care, or * suitable to receive a PD-1 inhibitor (pembrolizumab or nivolumab) as a standard of care in the discretion of the treating physician or Principal Investigator * Must have at least 1 target lesion that is clinically accessible to RiMO-301 injection and amenable to receive RT regimens specified in this protocol * The selected target lesions must be measurable on cross-sectional imaging and repeated measurements at the same location should be achievable * Target tumor not in the previously irradiated field or in the field irradiated at least six months prior to RiMO-301 injection and with no complications from the prior radiation course * RiMO-301 injection to multiple lesions (≤ 5 in total) in a single patient is allowed as long as the total tumor volume does not exceed 250 cm3 * Patient must have recovered from acute toxic effects (≤ grade 1 CTCAEv5) of previous cancer treatments prior to enrollment * Have adequate bone marrow reserve and adequate liver function * Have a life expectancy of at least 12 weeks * ECOG score of 0-2 * Age 18 years or older Exclusion Criteria: * Have signs or symptoms of end organ failure, major chronic illnesses other than cancer, or any severe concomitant conditions * Symptomatic central nervous system metastases and/or carcinomatous meningitis * Active autoimmune disease that has required systemic treatment in the past 2 years * Ongoing clinically significant infection at or near the incident lesion * Major surgery over the target area (excluding placement of vascular access) ≤21 days from beginning of the study drug or minor surgical procedures ≤7 days. No waiting is required following implantable port, enteral feeding tube and catheter placement * Has received any approved or investigational anti-neoplastic agent or immunotherapy other than PD-1 inhibitors (pembrolizumab or nivolumab) within 4 weeks prior to RiMO-301 injection * Patients with lesions which have significant blood vessel involvement (such as carotid artery encasement) or other major structures