Figure 1 PRISMA Flow Diagram.
Data extraction
Data extraction was undertaken by three reviewers (NK/RT). Key article information was uploaded into Microsoft Excel. Data extracted included study type, number of patients, method of biopsy including tonsillectomy or tongue base mucosectomy, surgical technique used, number of primary tumours detected and their location, human papillomavirus (HPV) status and use of any additional techniques such as frozen section.