Phase I study of bintrafusp alfa, a bifunctional fusion protein targeting TGF-β and PD-L1, in patients with pretreated biliary tract cancer ============================================================================================================================================ * Changhoon Yoo * Do-Youn Oh * Hye Jin Choi * Masatoshi Kudo * Makoto Ueno * Shunsuke Kondo * Li-Tzong Chen * Motonobu Osada * Christoph Helwig * Isabelle Dussault * Masafumi Ikeda