PIK3CA and esophageal squamous cell carcinoma: At the level of genetic alterations observed in single biochemical pathways, some pathways were similarly affected (cell cycle and epigenetic regulations); other pathways such as ERBB, RAS/RAF/MEK and TGF-β signaling were less mutated in ESCC than in EAC; finally, other pathways such as KEAP1/NRF2, NOTCH, FGF and PI3K/AKT/MTOR signaling were more mutated in ESCC than in EAC [61].