MPO and neoplasm: The number of tumour-infiltrating leukocytes present in HPV-negative or HPV-positive OPSCC was measured by immunohistochemical staining of TMA for myeloperoxidase (MPO; neutrophils), CD68 (macrophages) or CD3 (pan T cells) followed by QuPath image analysis and the percent number of positively stained cells as a proportion of the total number of cells in each core calculated (Supplementary Figure 1).