A Study of SYS6043 in Platinum-Resistant, Advanced Ovarian, Primary Peritoneal, or Fallopian Tube Cancers

Inclusion Criteria: 1. Female participants aged ≥ 18 years (as of the date of signed informed consent). 2. Histologically or cytologically confirmed epithelial ovarian cancer, fallopian tube cancer, or primary peritoneal cancer with a histologic subtype of high-grade serous carcinoma or G2-G3 endometrioid carcinoma. 3. Participants with prior platinum-based therapy and confirmed platinum-resistant recurrent disease, defined as disease progression or recurrence during platinum-based chemotherapy or within 6 months (183 days) after the last dose of platinum-based chemotherapy. A total number of treatment lines not exceeding 5 lines. 4. At least one evaluable extracranial lesion according to the Response Evaluation Criteria in Solid Tumors (RECIST v1.1). 5. Expected survival of the participant is ≥ 3 months. 5.6. For patients with previously confirmed folate receptor-α (FRα) positivity (verified by Ventana FOLR-2.1 assay: ≥75% of tumor cells exhibiting moderate \[2+\] or strong \[3+\] staining intensity per the PS2+ scoring method), prior treatment with mirvetuximab soravtansine is required, unless the investigator deems the patient intolerant to mirvetuximab soravtansine or the patient is ineligible for this therapy per the warnings in the prescribing information. 6.7. ECOG performance status 0-1, with no deterioration in ECOG score within 28 days prior to enrollment. 7.8. LVEF ≥ 50% as demonstrated by ECHO or MUGA obtained within 28 days before enrollment. 8.9. Major organ function must meet the following criteria within 7 days prior to enrollment: 1. Complete blood count (no whole blood, red blood cell, or platelet transfusion, and no administration of hematopoietic growth factors \[G-CSF or GM-CSF\], erythropoietin \[EPO\], or thrombopoietin \[TPO\] to correct blood cell counts within 7 days before sampling):i. Absolute neutrophil count (ANC) ≥ 1.5 × 10\^9/L;Platelet count (PLT) ≥ 100 × 10\^9/L;Hemoglobin (HGB) ≥ 90 g/L. 2. Blood biochemistry:i. Serum creatinine ≤ 1.5 × ULN;Serum total bilirubin (TBIL) ≤ 1.5 × ULN (participants with Gilbert's syndrome may be allowed up to 3 × ULN);Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 2.5 × ULN (≤ 5.0 × ULN for participants with hepatocellular carcinoma or liver metastasis);Serum albumin ≥ 30 g/L. 3\) Coagulation function: i. Activated partial thromboplastin time (APTT) and international normalized ratio (INR) ≤ 1.5 × ULN (for participants not receiving anticoagulation therapy; for those on anticoagulation therapy, levels must be within the therapeutic range with stable dose). 10\. Any toxicities related to prior therapy have resolved to CTCAE version 6.0 grade ≤1 or baseline level, excluding alopecia, fatigue, pigmentation, hypothyroidism stabilized with hormone replacement therapy, grade 2 peripheral neuropathy following chemotherapy, and other toxicities that the investigator deems not to pose a safety risk to participants. 11\. A sufficient washout period from prior anti-tumor therapy is required prior to the first study drug administration. 12\. Willing to provide a previously excised tumor sample or undergo a fresh tumor biopsy for the assessment of B7-H3 expression level (if no contraindications exist). 13\. Female participants of childbearing potential must have a negative serum pregnancy test within 7 days prior to randomization.Female participants of childbearing potential must agree to use highly effective contraception during the study and for at least 7 months after the last dose of study drug.Females must not be breastfeeding during this period.Females must not donate oocytes or undergo oocyte retrieval for personal use during this period. 14\. Provides voluntary written informed consent after adequate understanding of the clinical trial. Exclusion Criteria: 1. Patients with platinum-refractory disease (progression within 1 month after the last platinum-containing therapy). 2. Prior treatment with B7H3-targeted therapy. 3. Prior treatment with irinotecan, topotecan, any other topoisomerase I inhibitor (including investigational TOP1 inhibitors), or topoisomerase inhibitor-antibody drug conjugate (e.g., trastuzumab deruxtecan, etc.). 4. Patients for whom paclitaxel, topotecan, and pegylated liposomal doxorubicin (as listed in the control group) are all considered inappropriate by the investigator. 5. History of severe cardiac or cerebrovascular disease, including but not limited to: heart failure ≥ New York Heart Association (NYHA) Class 2; acute coronary syndrome (e.g., myocardial infarction, unstable angina, etc.) within 6 months prior to screening; acute cerebrovascular disease (e.g., transient ischemic attack, cerebral infarction, cerebral hemorrhage, etc.) within 6 months prior to screening. 6. Mean corrected QT interval using the Fridericia formula (QTcF) \> 470 milliseconds (ms) based on the results of three 12-lead electrocardiogram (ECG) examinations; history of serious cardiac arrhythmia (e.g., complete left bundle branch block, third-degree atrioventricular block, atrial fibrillation, atrial flutter, ventricular fibrillation, ventricular flutter, etc.), excluding transient atrial fibrillation and atrial flutter. 7. Unable or unwilling to discontinue concomitant medications known to prolong the QT interval. 8. A history of or current interstitial lung disease (ILD) requiring glucocorticoid treatment, non-infectious interstitial pneumonia, pulmonary fibrosis, and radiation pneumonitis requiring hormone treatment, or suspected of having such diseases by imaging examination at the time of screening. 9. A history of underlying lung diseases, including but not limited to pulmonary embolism within 3 months prior to the start of study treatment, severe asthma, severe COPD, restrictive lung disease, and other clinically significant lung damage or requiring supplementary oxygen. 10. Patients with active pulmonary tuberculosis (those who have rece