Inclusion Criteria:  histopathologic diagnosis of squamous cell carcinoma of the head and neck primary radio(chemo)therapy with curative intent available pretherapeutic FDG-PET/CT imaging available pretherapeutic differential blood analysis  Exclusion Criteria:  other tumor entities of the head and neck including cutaneous squamous cell carcinoma primary surgical treatment ongoing infections or other inflammatory diseases at the time of diagnosis patients not completing a course of irradiation with at least 66 Gray locally