APOBEC3A and esophageal squamous cell carcinoma: Only the datasets from healthy tonsil and oesophagus and from HNSCC and ESCC contained sufficient APOBEC3A and/or APOBEC3B expressing cells to permit further analysis, so we initially interrogated the data from tonsil epithelial cells, the dataset in which we observed the highest average APOBEC3A expression per cell and the greatest proportion of APOBEC3A- and/or APOBEC3B-positive cells (Fig. 1).