Dramatically inferior outcomes for patients with HPV33-related HNSCC compared to HPV16-related HNSCC have been noted by Chatfield-Reed et al. [37], who paid attention to the specific signatures of APOBEC enzymes (a family of cytidine deaminases that promote the conversion of deoxycytidine to deoxythymidine), which have previously been shown to regulate innate antiviral immunity, including that for HPV [38]. Here, CDA is linked to head and neck squamous cell carcinoma.