Testing Mitazalimab in Combination With Standard Chemotherapy in Immunotherapy Resistant Advanced Biliary Tract Cancers

The goal of this clinical trial is to etablish whether adding Mitazalimab to standard chemotherapy is more effective than standard chemotherapy alone in people with advanced bile duct cancer. It will also learn about the safety of Mitazalimab. The main questions it aims to answer are: * Does the addition of Mitazalimab enhance efficacy? * What medical problems do participants have when taking Mitazalimab + mFOLFOX? Participants will: * Take drug mFOLFOX every two weeks until disease progression or mFOLFOX every two weeks plus mitazalimab in addition to mFOLFOX, with a first injection 7 days before the first mFOLFOX chemotherapy and then 3 days after the start of each mFOLFOX cycle. * Visit the clinic once every 2 weeks for checkups and tests * Have a radiological assessment every 8 weeks during treatment. After stopping treatment, participants will be monitored at the hospital every 8 weeks if no progression is observed, or every 12 weeks after disease progression.

Multicenter, open-label, randomized phase II/III trial evaluating the efficacity of mitazalimab in combination with mFOLFOX compared to mFOLFOX alone in participant advanced BTC