APOBEC3A and head and neck squamous cell carcinoma: Having confirmed specificity by staining of paraffin-embedded blocks generated from PMA-treated wild-type control and APOBEC3A-knockout (KO) NIKS (Appendix Fig. S14), we conducted APOBEC3A immunohistochemistry on a tissue microarray (TMA) representing 20 HNSCC cases (10 HPV+ve and 10 HPV−ve).