The primary objectives of this study are as follows: Phase 1 (sequential dose-escalation): to evaluate the safety and tolerability of sacituzumab govitecan-hziy (SG) as a single agent and to determine the recommended Phase 2 dose (RP2D) of SG in Japanese participants with advance solid tumors. Phase 2: Evaluate the safety and efficacy of SG in Japanese participants with metastatic triple-negative breast cancer (mTNBC), hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (mBC), and metastatic urothelial cancer (mUC).