TP53 and esophageal squamous cell carcinoma: Overall, mutations attributable to endogenous mutagenic processes were infrequent; for example, G∶C to A∶T mutations at CpG sites, a type of mutation which often occurs as the result of spontaneous deamination of 5′methylcytosine, represented only 13.3% of all mutations, in contrast to 25% of mutations in all cancers compiled in the TP53 mutation database (n = 26597) and 33% of the mutations in ESCC cases from Tehran (n = 85) [14], [15].