In a multicenter study in Japan (PRELUDE study) [17], we analyzed 423 patients with advanced BTC using the break-apart FISH method and found that 7.7% of iCCA and 4.8% of perihilar cholangiocarcinoma (PCC) cases were positive for the FGFR2 fusion gene. The gene discussed is FGFR2; the disease is hilar cholangiocarcinoma.