525 Safety and efficacy of pembrolizumab (MK-3475) in patients (pts) with advanced biliary tract cancer: Interim results of KEYNOTE-028. (September 2015) - Bang, Y.J.; Doi, T.; Braud, F. De; Piha-Paul, S.; Hollebecque, A.; Razak, A.R. Abdul; Lin, C.C.; Ott, P.A.; He, A.R.; Yuan, S.S.; Koshiji, M.; Lam, B.; et al.