This study is testing new cancer treatments for advanced biliary tract cancer (BTC) that shows a protein called HER2. **Biliary tract cancer** affects the tubes that carry bile (a fluid that helps digest food) from the liver to the small intestine. Key points: - **Length & Visits**: The study involves regular doctor visits and tests to check your health and how the treatment works. - **Risks**: Some risks include common side effects of cancer treatments, like feeling tired or sick. Your doctor will explain all possible risks. - **Compensation**: Participants may receive compensation for their time and travel. To join, you must be 18 or older and have HER2-expressing BTC that cannot be removed by surgery and hasn't been treated with certain cancer drugs before. If you have certain heart, lung, or other serious health conditions, you might not be able to participate. You need to provide a recent tumor sample for testing and meet other health criteria, like having good organ function and a minimum life expectancy of 12 weeks. Always discuss with your doctor to see if joining this study is right for you.