Phosphoinositide-3-kinase, regulatory subunit 3 (gamma) (PIK3R3, p55PIK) is a regulatory subunit of phosphoinositide 3-kinase (PI3K) and is involved in ICC hyperplasia which is prone to the tumorigenesis of GIST [32, 165]. The gene discussed is PIK3R3; the disease is intrahepatic cholangiocarcinoma.