UBR5 and esophageal squamous cell carcinoma: Similarly, we found a significant increase in the contribution of APOBEC signatures (SBS2*, SBS13*) in ESCC samples with PIK3CA mutations, and the other three genes (ARHGAP5, SETD2, and UBR5) were also associated with APOBEC signature (SBS13*) (Figure 4F, Figure S8A).