Other signatures of mutation identified in HNSCC include those associated with age and natural variation in the genome23–25, COSMIC signatures 1 and 5, as well as endogenous deaminases of the AID (activation-induced cytidine deaminase) and APOBEC (apolipoprotein B mRNA editing enzyme, catalytic polypeptide) family20,26,27. Here, AICDA is linked to head and neck squamous cell carcinoma.