Pamiparib and Low Dose Temozolomide In Patients With Platinum Sensitive Biliary Tract Cancer

The main objective of this trial is to evaluate the activity of pamiparib plus low dose TMZ as maintenance treatment in improving progression free survival (PFS) in patients with advanced BTC who have received first line platinum-based chemotherapy. The primary objective is to test with a one-sided type I error of 10% whether pamiparib plus low dose TMZ as maintenance treatment increases PFS according to RECIST (version 1.1) in the entire study population as compared to standard treatment with Cisplatin-Gemcitabine chemotherapy regimen (or Gemcitabine-Oxaliplatin if cisplatin is contra-indicated). This is an open label randomized controlled multi-center phase II trial. Patients must meet all the criteria to be eligible. Eligible patients will be centrally randomized between the two arms in a 1:1 ratio. Randomization will be stratified by the following factors: * Tumour response CR/PR vs SD vs non-measurable/non-PD after previous platinum-based chemotherapy as confirmed by central review * Tumour location (intrahepatic bile ducts vs. gallbladder vs. perihilar bile ducts and distal bile duct and /ampulla of Vater tumours). Patients will receive treatment until progression or for a maximum period of 2 years.