This report describes treatment of locoregional head and neck squamous cell carcinoma (HNSCC) by an innovative, experimental strategy involving generation of a robust anti-cancer agent (2-fluoroadenine [F-Ade]) following transduction by Escherichia coli purine nucleoside phosphorylase (PNP) in a small number of tumor cells. F-Ade works by a unique mechanism of action (ablation of RNA and protein synthesis) and confers tumor regressions of otherwise refractory HNSCC in human subjects. Clinical studies have now advanced to a pivotal (registration-directed) trial involving locoregional HNSCC, with plans to begin subject enrollment late in 2018. The present review is the first to summarize use of PNP in the context of HNSCC, and provides background regarding this emerging anti-cancer approach.