APOB and esophageal squamous cell carcinoma: Six mutational signatures (SBS1, SBS2, SBS5, SBS13, SBS18 and SBS40) account for more than 80% of the mutational burden of ESCC, with apolipoprotein B mRNA editing enzyme, and catalytic polypeptide-like (APOBEC)-associated signatures being present in approximately 90% of cases, supporting the contention that APOBEC alterations are fundamental in the development of ESCC [60].