Combining Pembrolizumab and Metformin in Metastatic Head and Neck Cancer Patients

Inclusion Criteria: * Histologically or cytologically confirmed recurrent or metastatic non-cutaneous HNSCC for which there are no surgical or radiation curative options. * Patients may have received up to 3 prior lines of therapy for metastatic or recurrent disease. * ECOG performance status ≤2 Exclusion Criteria: * Patients with nasopharyngeal HNSCC will be excluded * Patients who have had chemotherapy or radiotherapy within 2 weeks prior to entering the study. * Patients who have not recovered from adverse events due to prior anti-cancer therapy * Patients who have previously received PD-1 or PD-L1 inhibitors for metastatic/recurrent disease * Patients currently receiving metformin or who have received metformin in the last 6 months