Sacituzumab Tirumotecan vs MMAE-ADCs in Advanced Urothelial Carcinoma (FUSCC-SPARE-UC-01)

The main goal of this clinical trial is to learn if a new targeted cancer drug called sacituzumab tirumotecan (sac-TMT) works to treat cancer while causing less nerve damage in patients with advanced urothelial carcinoma who have progressed on or could not tolerate previous treatment such as enfortumab vedotin plus pembrolizumab (EVP) or disitamab vedotin plus toripalimab (DVT). The main question it aims to answer is: Does sac-TMT lower the risk of getting severe nerve damage, as measured together by doctors, machines, and the participants? Researchers will compare sac-TMT to alternative MMAE-based ADC drugs (switching to a different MMAE-based ADC after the first one stopped working) to see if sac-TMT causes less nerve damage while still effectively treating the cancer. A small group of participants who had to stop their previous MMAE-based ADC treatment because of nerve damage will also receive sac-TMT to learn if the drug is safe for their nerves. Participants will: 1. Receive either sac-TMT or another MMAE-based ADC drug 2. Have regular physical exams by a doctor to check their nerves 3. Have machine tests to measure how well their nerves work 4. Answer survey questions about their pain, numbness, and daily activities

Inclusion Criteria 1. Must voluntarily sign the written Institutional Review Board (IRB)/Ethics Committee (EC) approved informed consent form (ICF) prior to any screening procedures. 2. Age \> 18 years at the time of signing the ICF. 3. Histologically or cytologically confirmed locally advanced (unresectable) or metastatic urothelial carcinoma (UC), including bladder, ureter, renal pelvis, or urethra. Participants with mixed histology are eligible provided that UC is the predominant component (\> 50%). 4. Must have received at least one prior line of systemic therapy for locally advanced or metastatic UC (e.g., Enfortumab Vedotin plus Pembrolizumab, Disitamab Vedotin plus Toripalimab, platinum-based chemotherapy, immune checkpoint inhibitors, Nectin-4 ADCs, HER2 ADCs, FGFR inhibitors, or other palliative chemotherapy regimens). 5. Neuropathy Status: Cohort A/B: Baseline peripheral neuropathy (PN) Grade 0-1 (per NCI-CTCAE v5.0) with stable nerve function confirmed by Nerve Conduction Study (NCS) during screening. Cohort C (Observational): Baseline PN Grade 2, or a history of PN \> Grade 2 where the investigator deems the patient unsuitable for MMAE-based ADC treatment. 6. At least one measurable lesion per RECIST v1.1. (Lesions in previously irradiated areas are considered target lesions only if clear progression is documented after radiotherapy). 7. ECOG Performance Status of 0 or 1 at screening. 8. Expected survival \> 3 months. 9. Must have adequate organ and bone marrow function (no blood transfusion, growth factors, or albumin support within 14 days prior to screening): * Hematological: ANC \>= 1.5 x 10\^9/L; Platelets \>= 75 x 10\^9/L; Hemoglobin \>= 90 g/L. * Hepatic: ALT and AST \