This is an open-label, multi-center, multi-cohort, Phase 2 study to evaluate the efficacy and safety of trastuzumab deruxtecan (T-DXd) for the treatment of selected HER2-expressing tumors. This study will consist of Part 1 which includes 7 cohorts of: urothelial bladder cancer, biliary tract cancer, cervical cancer, endometrial cancer, ovarian cancer, pancreatic cancer, and rare tumors; and Part 2 which includes 5 cohorts A to E of: A) any tumor type that is HER2 IHC 3+ (excluding breast, gastric cancer, and colorectal cancer), B) any tumor type that is HER2 IHC 2+/ISH+ (excluding breast, gastric cancer, and colorectal cancer), C) HER2 IHC 2+ or 1+ endometrial cancer, D) HER2 IHC 2+ or 1+ ovarian cancer, and E) HER2 IHC 2+ or 1+ cervical cancer. Study hypothesis: Trastuzumab deruxtecan will show meaningful clinical activity and a favorable risk benefit profile in selected HER2-expressing solid tumors.