Differences in the amplification frequency between ESCC and EADC have also been reported from other genes, including SOX2, PIK3CA, MYC, CCND1, which had a higher amplification frequency in ESCC, and GATA4 as well as GATA6, which had a higher amplification frequency in EADC [25]. Here, PIK3CA is linked to esophageal squamous cell carcinoma.