Sacituzumab Govitecan Plus EV in Metastatic UC

Phase II Study Cohort A (dose expansion study to assess efficacy of Sacituzumab Govitecan (SG) and Enfortumab vedotin-ejfv (EV) combination) Inclusion Criteria: * Participants must have histologically documented confirmed predominant urothelial carcinoma (i.e. of the bladder, renal pelvis, ureter or urethra). Patients with squamous differentiation or mixed cell types are eligible if the urothelial component is more than 50%; small-cell carcinoma is not allowed. Patients with locally advanced unresectable disease are eligible. * Patient who are cisplatin eligible must have received prior treatment with platinum containing therapy defined as within the adjuvant/neoadjuvant setting with ≥ ypT2 disease at surgery or recurrent or progressive disease within 12 months or receiving treatment with platinum in locally advanced or metastatic setting. In addition, they must have received a checkpoint inhibitor (CPI) in locally advanced or metastatic urothelial cancer setting. Patients who received CPI therapy in the neoadjuvant/adjuvant setting and had recurrent or progressive disease either during or within 12 months of therapy completion are eligible. A CPI is defined as a PD-1 or PD-L1 inhibitor. * Patients who are cisplatin-ineligible need only have progressed on or since one line of therapy defined as therapy given in the adjuvant/neoadjuvant setting within 12 months of progression or receiving therapy for locally advanced or metastatic disease * Patient must be progressing on or since most recent therapy * Age ≥18 years. Children are excluded from this study, but will be eligible for future pediatric trials. * ECOG performance status 0-1. * Participants must have adequate organ and marrow function as defined below: * Leukocytes ≥3,000/mcL * Absolute neutrophil count ≥1,500/mcL * Platelets ≥100,000/mcL * Total bilirubin ≤ institutional upper limit of normal (ULN) * AST(SGOT)/ALT(SGPT) ≤2.5x institutional ULN OR * ≤5x ULN with liver metastases and serum albumin \> 3 g/dL * Glomerular filtration rate (GFR) ≥30 mL/min/1.73 m2 (by Cockcroft Gault formula) * Human immunodeficiency virus (HIV)-infected participants on effective anti-retroviral therapy with undetectable viral load within 6 months are eligible for this trial. * For participants with evidence of chronic hepatitis B virus (HBV) infection, the HBV viral load must be undetectable on suppressive therapy, if indicated. * Participants with a history of hepatitis C virus (HCV) infection must have been treated and cured. For participants with HCV infection who are currently on treatment, they are eligible if they have an undetectable HCV viral load. * Participants with known history or current symptoms of cardiac disease, or history of treatment with cardiotoxic agents, should have a clinical risk assessment of cardiac function using the New York Heart Association Functional Classification. To be eligible for this trial, participants should be class 2B or better. * Have measurable disease by computed tomography (CT) or magnetic resonance imaging (MRI) as per response evaluation criteria in solid tumors version 1.1 (RECIST 1.1 criteria). Tumor lesions situated in a previously irradiated area are considered measurable if progression has been demonstrated in such lesions * Female subjects of childbearing potential must have a negative urine or serum pregnancy test within 72 hours prior to receiving the first dose of study medication. If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required * Female subjects of childbearing potential must be willing to use 2 methods of birth control or be surgically sterile or abstain from heterosexual activity for the course of the study through 6 months after the last dose of study medication. Subjects of childbearing potential are those who have not been surgically sterilized or have not been free from menses for \>2 years * The effects of SG and EV on the developing human fetus are unknown. Women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation and 6 months after last study drug. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study and up to 6 months after last study drug dose, she should inform her treating physician immediately. Men treated or enrolled on this protocol must also agree to use adequate contraception prior to the study, for the duration of study participation, and 4 months after completion of SG administration. * Ability to understand and the willingness to sign a written informed consent document. Exclusion Criteria: Subjects meeting any of the following exclusion criteria at Screening/Day 1 of treatment will not be enrolled in the study. * Women who are pregnant or lactating. Pregnant women are excluded from this study because SG and EV have potential for teratogenic or abortifacient effects. Because there is an unknown but potential risk for adverse events in nursing infants secondary to treatment of the mother with EV or SG, breastfeeding should be discontinued if the mother is treated on protocol. * Have had a prior anti-cancer biologic agent (including immune checkpoint inhibitors) within 4 weeks prior to Cycle 1 Day 1 (C1D1) or have had prior chemotherapy, targeted small molecule therapy, or radiation therapy within 2 weeks prior to C1D1. Subjects participating in observational studies are eligible. * Presence of any toxicities attributed to prior anti-cancer therapy that are not resolved to Grade 1 or baseline that could impose serious risk for complications before administration of study drug agent * Note: If subjects received major surgery, they must have recovered adequately from the toxicity and/or complications from the intervention prior to starting therapy. * Have previously received topoisomerase 1 inhibitors, SG or EV