KRAS and cholangiocarcinoma: Similarly, Andersen and Jakobsen [28] tested a multiplex digital PCR method to search for mutations in KRAS, NRAS proto-oncogene (NRAS), BRAF, and phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) genes in the plasma of 5 CCA patients with known tumor tissue mutations and found that the mutations present in the tumor were also detected in plasma samples in 100% of cases.