PIK3CA and biliary tract cancer: Significant mutations occurred in 32 genes, including KRAS, PIK3CA, IDH1, NRAS, guanine nucleotide binding protein, alpha stimulating activity polypeptide (GNAS), and ERBB2. Among these, TP53, BRCA1, BRCA2, and PIK3CA were observed as gene mutations common to the biliary tract cancers.