PIK3C2A and esophageal squamous cell carcinoma: In general, the genetic alterations of PIK3CA (24%), and PTEN (7%) are observed in ESCA (Table 1), especially the somatic mutations of PIK3CA (7.2% vs 12.5%), PIK3C2A (0.7% vs. 0), PIK3CG (2.9% vs. 4.2%) and PIK3C2G (0 vs. 37.5%) are observed respectively in 139 paired ESCC cases and 24 cell lines [98].