Study of Sacituzumab Govitecan (SG) in Japanese Participants With Advanced Solid Tumors

Key Inclusion Criteria: * Eastern Cooperative Oncology Group (ECOG) performance status ≤ 1 * Measurable disease by computed tomography (CT) or magnetic resonance imaging (MRI) as per RECIST Version 1.1 criteria * Adequate hematologic counts without transfusional or growth factor support within 2 weeks of study drug initiation * Adequate hepatic function (bilirubin ≤ 1.5 upper limit of normal (ULN)), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 2.5 ULN * Creatinine clearance ≥ 30 mL/min * Male and female individuals of childbearing potential who engage in heterosexual intercourse must agree to use protocol-specified method(s) of contraception. * Phase 1 only: Histologically or cytologically confirmed advanced solid tumor that is refractory to or intolerant of all standard therapy or for which no standard therapy is available. * Phase 2 metastatic triple-negative breast cancer (mTNBC) Cohort: Histologically or cytologically confirmed TNBC per American Society of Clinical Oncologists/College of American Pathologists (ASCO/CAP) criteria, based on the most recent analyzed biopsy or other pathology specimen. Refractory to or relapsed after at least 2 prior standard-of-care chemotherapy regimens for unresectable, locally advanced or metastatic breast cancer. * Phase 2 hormone receptor-positive/human epidermal growth factor receptor 2-negative metastatic breast cancer (HR+/HER2- mBC) Cohort: Documented evidence of HR+/HER2- mBC confirmed by a local laboratory and defined per ASCO/CAP criteria. * Refractory to or relapsed after 2 prior systemic chemotherapy regimens for locally advanced unresectable or metastatic disease. * Phase 2 metastatic urothelial cancer (mUC) Cohort: Histologically documented UC that is metastatic or locally advanced unresectable. * Progressed or recurred following receipt of platinum-containing regimen and anti-PD-1/PD-L1 therapy for metastatic or locally advanced unresectable disease Key Exclusion Criteria: * Positive serum pregnancy test, or females who may possibly be pregnant * Known Gilbert's disease * Have previously received antibody drug conjugate containing topoisomerase I inhibitors * Presence of bulky disease (defined as any single mass \> 7 cm in greatest dimension). * Known to be HIV positive, or hepatitis B virus (HBV) surface antigen positive or hepatitis C virus (HCV) antibody positive at screening * Known history of significant cardiac disease * Known history of clinically significant active chronic obstructive pulmonary disease, or other moderate-to-severe chronic respiratory illness * History of interstitial lung disease * History of clinically significant gastrointestinal (GI) bleeding, have active chronic inflammatory bowel disease (ulcerative colitis, Crohn's disease) or GI perforation * Individuals with a history of anaphylactic reaction to irinotecan. Note: Other protocol defined Inclusion/Exclusion criteria may apply.