PARP1 and head and neck squamous cell carcinoma: In this study, we have now examined the comparative effect of photons (x-rays) on 3D spheroid models of HPV-positive and HPV-negative OPSCC and also the impact of the PARP inhibitors olaparib and talazoparib in sensitising an extended panel of radioresistant HPV-negative HNSCC models to both photons and proton beam therapy.