An example of these genes is the PI3K’s p110 catalytic subunit PIK3CA, which is the third most frequently mutated gene in GC following tumor protein 53 (TP53) and AT-rich interactive domain-containing protein 1A (ARID1A) and has been implicated as an oncogene in various cancers [23,214,215]. The gene discussed is PIK3CA; the disease is cancer.