PIK3CA and gastric cancer: It was known that mutations in genes such as CDH1 (Kaurah et al., 2007; Corso et al., 2012; Chen et al., 2013), PIK3CA (Samuels et al., 2004; Li et al., 2005; Velho et al., 2005; Lee et al., 2012), ARID1A (AT-rich interactive domain 1A) (Zang et al., 2012), EGFR (Corso et al., 2011; Liu et al., 2011), and PTEN (Heald et al., 2010; Wen et al., 2010) existed in gastric cancer, providing potential circulating DNA for detection of gastric cancer.