BL-M07D1 (Trastuzumab Brengitecan T-bren) vs Standard of Care Platinum-based Chemotherapy (PBC) for HER2-expressing Metastatic Urothelial Cancer After Progression on Anti-PD-(L)1-based Therapy

Inclusion Criteria: * Histologically or cytologically documented metastatic or surgically unresectable transitional cell carcinoma (TCC) of the urothelium involving the renal pelvis, ureter, bladder, or urethra. Minor histologic variants (ie, \<50% overall) are acceptable, provided that TCC is the dominant histology. * Disease progression or recurrence during or following anti-PD-(L)1-based therapy. * Fresh biopsy or archival tumor samples. * Documented HER2 expression by central laboratory testing. * Eligible to receive carboplatin or cisplatin in combination with gemcitabine. * At least 1 measurable lesion based on RECIST v1.1. * An Eastern Cooperative Oncology Group performance status (ECOG PS) of 0 to 1. * Adequate organ function. * Adequate coagulation parameters. Exclusion Criteria: * Prior topoisomerase inhibitor-based ADC therapy. * Primary tumors in the central nervous system (CNS), active or untreated CNS metastases, or carcinomatous meningitis. * Bladder cancers with small cell histology. * Other prior or concurrent malignancies except for certain localized cancers or low-grade prostate cancer (if approved by sponsor), or other malignancy treated with curative intent with a disease-free interval of at least 3 years. * Prior history of clinically significant bleeding, or perforation of the gastrointestinal tract within 6 months of randomization. * Active autoimmune diseases and inflammatory diseases. * History of noninfectious interstitial lung disease (ILD)/pneumonitis that required treatment with steroids, have current ILD/pneumonitis, or where suspected ILD/pneumonitis cannot be ruled out by imaging at Screening. * Advanced/clinically significant lung disease (eg, poorly controlled chronic obstructive pulmonary disease or asthma, restrictive lung disease, or pulmonary hypertension) within 6 months prior to randomization. * Known human immunodeficiency virus infection. * Active hepatitis B virus (HBV) infection. * Active hepatitis C virus (HCV) infection. * Active or latent tuberculosis. * Other protocol-specified inclusion/ exclusion criteria apply