Given the considerable evidence linking APOBEC3A-mediated mutagenesis to deamination of the lagging strand during DNA replication (Green et al, 2016; Haradhvala et al, 2016; Hoopes et al, 2016; Morganella et al, 2016; Seplyarskiy et al, 2016; Stewart et al, 2020), we used gene expression data to assign cells from our normal tonsil and HNSCC datasets to G0/G1, S, or G2/M phase of the cell cycle (Fig. 5F inset) and compared APOBEC3A expression and GRHL3 activity in those cells predicted to be in S-phase. Here, GRHL3 is linked to head and neck squamous cell carcinoma.