Additionally, 9.5% (13/137) of biliary tract cancer (BTC) patients including those with CC have mutations in exon 20 and exon 21 in patients with ICC (T783I, S784F, D837N), ECC (D800G, C818R, V819M, Q820R, D837N, V851I, G873E, G874D), or GBC (A837N, T785I) [108], which correspond with the kinase domain of EGFR [108]. Here, EGFR is linked to cholangiocarcinoma.