A Single-Center, Open-Label, Single-Arm, Phase I Study With Dose Expansion Cohort of Sacituzumab Govitecan in Combination With Cisplatin in Platinum Sensitive Recurrent Ovarian and Endometrial Cancer

Eligibility waivers are not permitted. Subjects must meet all of the inclusion and exclusion criteria to be registered to the study. Study treatment may not begin until a subject is registered. Inclusion Criteria: * Pathologic (histology or cytology) confirmed diagnosis of epithelial ovarian cancer or endometrial cancer * Radiographic evidence of recurrent epithelial ovarian cancer (ovarian, fallopian tube, or primary peritoneal cancer) or endometrial cancer that is "platinum-sensitive," defined as progression of disease beyond 6 months from the last dose of platinum-based chemotherapy * Female, age ≥ 18 years * World Health Organization (WHO) performance status 0-1 with no deterioration over the previous 2 weeks and minimum life expectancy of 12 weeks * Patient has measurable disease (at least one lesion that can be accurately assessed repeatedly by CT) as evidenced on pre-treatment baseline CT of Chest/Abdomen/Pelvis or PET/CT, or evaluable disease * Adequate hematologic counts, as defined below, without transfusion or growth factor support within 2 weeks of study drug initiation: * Hemoglobin ≥ 8.5 g/dL * Absolute neutrophil count ≥ 1500/mm3 * Platelets ≥ 100,000/μL * Adequate organ function as defined below: * Total bilirubin ≤ 1.5 ULN * AST(SGOT)/ALT(SPGT) ≤ 2.5x ULN or ≤ 5 x ULN if known liver metastases * Serum albumin \> 3 g/dL * Creatinine clearance ≥ 50 mL/min per the Cockcroft-Gault equation * Women of childbearing potential must agree to use adequate contraception prior to study entry, for the duration of study participation, and for 6 months following completion of therapy. Should a woman become pregnant or suspect she is pregnant while participating in this study, she should inform her treating physician immediately. o A female of child-bearing potential is any woman (regardless of sexual orientation, having undergone a tubal ligation, or remaining celibate by choice) who meets the following criteria: * Has not undergone a hysterectomy or bilateral oophorectomy; or * Has not been naturally postmenopausal for at least 12 consecutive months (i.e., has had menses at any time in the preceding 12 consecutive months). * Ability to understand and the willingness to sign a written informed consent. Exclusion Criteria: Treatment with any of the following: * Any investigational agents or study drugs from a previous clinical study within 28 days or 5 half-lives (whichever is longer) of the first dose of study treatment * Any other chemotherapy, immunotherapy or anticancer agents within 14 days of the first dose of study treatment * Major surgery (excluding placement of vascular access) within 4 weeks of the first dose of study treatment * Radiotherapy with a wide field of radiation within 4 weeks or radiotherapy with a limited field of radiation for palliation within 2 weeks of the first dose of study treatment * With the exception of alopecia, any unresolved toxicities from prior therapy greater than Common Terminology Criteria for Adverse Events (CTCAE) grade 1 at the time of starting study treatment * As judged by the investigator, any evidence of severe or uncontrolled systemic diseases, including active bleeding diatheses, or uncontrolled infection including hepatitis B, hepatitis C and human immunodeficiency virus (HIV). Screening for chronic conditions is not required. * Known or severe (Grade 3 or higher) hypersensitivity to SG and/or cisplatin, their metabolites, or formulation excipients * Peripheral neuropathy grade 2 or greater * Refractory nausea and vomiting, chronic gastrointestinal diseases * Patients must not be pregnant or nursing due to the potential for congenital abnormalities and the potential of this regimen to harm nursing infants. * Women of childbearing potential unwilling to use effective contraception during study until conclusion of 6-month post-treatment evaluation period * Known history of unstable angina, MI, or CHF present within 6 months of randomization or clinically significant cardiac arrhythmia (other than stable atrial fibrillation) requiring anti-arrhythmia therapy * Known history of clinically significant active COPD, or other moderate-to-severe chronic respiratory illness present within 6 months of enrollment. * Prior history of clinically significant bleeding, intestinal obstruction, or GI perforation within 6 months of enrollment. * Other concurrent medical or psychiatric conditions that, in the Investigator's opinion, may be likely to confound study interpretation or prevent completion of study procedures and follow-up examinations. * Prior therapy with sacituzumab govitecan, irinotecan, Trop-2-directed antibody drug conjugate, or any topoisomerase I-containing antibody-drug conjugates at any time for early stage disease * Have active chronic inflammatory bowel disease (ulcerative colitis, Crohn's disease) or GI perforation within 6 months of enrollment. * Requirement for ongoing therapy with any prohibited medications * Have known active central nervous system (CNS) metastases and/or carcinomatous meningitis. Participants with previously treated brain metastases may participate provided they have stable CNS disease for ≥ 4 weeks prior to randomization and all neurologic symptoms have returned to baseline, have no evidence of new or enlarging brain metastases, and are taking 10 mg/day or less of prednisone or its equivalent. All participants with carcinomatous meningitis are excluded regardless of clinical stability. * Have an active second malignancy. Participants with a history of malignancy that have been completely treated, with no evidence of active cancer for 3 years prior to randomization, or participants with surgically cured tumors with low risk of recurrence (e.g., nonmelanoma skin cancer, histologically confirmed complete excision of carcinoma in situ, or similar) are allowed to enroll. * Use of any live vaccine against infectious diseases within 30 days of the first dose of study drugs. * Have an active serious infection requiring systemic antimicrobial therapy