PRF1 and head and neck squamous cell carcinoma: Although there exists a spectrum of immune cell infiltrates in HNSCC, it is now recognised that HPV‐positive and HPV‐negative HNSCCs have distinctly different immunophenotypes characterised by increased T‐cell infiltrate, more immune cells expressing PD‐L1 and increased presence of markers of immune activation (eg granzyme and perforin) in HPV‐positive tumours whilst HPV‐negative tumours tend to have less abundant immune cell infiltrates including T cells and Tregs.67