ARID1A and intrahepatic cholangiocarcinoma: Exon sequencing data from MSKCC demonstrated that genes frequently implicated as oncogenic drivers, such as KRAS, BRAF, FGFR2 TP53, CDKN2A, IDH1, IDH2, and NRAS, were infrequently mutated in the early-onset ICC patients, whereas genes, such as BAP1, ARID1A, and PBRM1, that were mostly mutated in late-onset ICC, were rarely mutated in the early-onset ICC cohort (Fig. 4b).