A Study of SKB518 as Monotherapy or Combination Therapy in Patients With Advanced Gynecological Malignant Tumors

Inclusion Criteria: 1. Provide signed written informed consent and demonstrate understanding of and agreement to comply with study requirements and the study visit schedule. Age 2. Be ≥ 18 years and ≤ 75 years of age at the time of informed consent signing. Participant Type and Disease Characteristics 3. Have an Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) of 0 or 1 within 2 weeks prior to first dose administration. 4. Have a cytologically or histologically confirmed gynecologic malignancy. * Cohort A: Ovarian cancer (OC) (including fallopian tube cancer and primary peritoneal cancer) with epithelial ovarian carcinoma histology, previously treated with 2-4 lines of systemic therapy, excluding primary platinum-resistant ovarian cancer (defined as disease recurrence or progression during first-line platinum-containing therapy, or disease recurrence or progression occurring \<182 days from the last platinum-containing therapy in the first line). * Cohort B: Cervical cancer or endometrial cancer that has failed standard therapy or is intolerant to standard therapy, or for which no standard therapy exists. * Cohort C: Platinum-sensitive ovarian cancer (PSOC) previously treated with 2-4 lines of systemic therapy. * Cohort D: PSOC previously treated with 1-2 lines of systemic therapy. * Cohort E Safety Lead-in Phase: PSOC previously treated with 2-4 lines of systemic therapy. * Cohort E Expansion Phase: PSOC participants who have achieved Complete Response (CR),Partial Response (PR), or Stable Disease (SD) after 2 lines of therapy (platinum-based doublet regimen combined with bevacizumab), and require randomization within 8 weeks after the last dose. Participants in Cohorts A, C, D, and E with known breast cancer susceptibility gene (BRCA) mutations must have received poly(ADP-ribose) polymerase (PARP) inhibitor therapy, unless contraindicated. Note: 1. PSOC is defined as radiographic progression/recurrence occurring ≥6 months after the last platinum-containing chemotherapy, i.e., the interval from the date of the last platinum therapy to radiographic evidence of disease progression per RECIST v1.1 should be ≥6 months (182 days). 2. Line counting rules for OC are as follows: * Adjuvant ± neoadjuvant therapy is considered 1 line of systemic antineoplastic therapy. * Maintenance therapy (e.g., bevacizumab, PARP inhibitors) as part of frontline antineoplastic therapy is not counted as a separate line. * Treatment regimen changes due to intolerance toxicity rather than disease progression are considered part of the same prior treatment line and are not counted as a separate line. 5. Provide approximately 10-13 unstained consecutive tumor tissue slides during the screening period for gene expression level testing (preferably from recently obtained tissue). If fresh tumor tissue samples are unavailable, archived tumor tissue samples obtained within 2 years prior to first study dose administration may be provided. If a participant is unable to provide archived tumor tissue samples within 2 years prior to first dose, or unable to provide a sufficient number of unstained consecutive tumor tissue slides, the investigator must discuss with the medical monitor to determine whether earlier obtained tumor tissue samples or a reduced number of slides may be accepted. Fine-needle aspiration biopsy specimens or core biopsies are insufficient for biomarker testing. Cell smears from centrifuged thoracic/abdominal/pelvic/pericardial effusion drainage, and bone lesions without soft tissue components or from decalcified bone tumor specimens are also unacceptable. 6. Have at least one target lesion per RECIST v1.1 criteria, accurately measured at baseline by computed tomography (CT) or magnetic resonance imaging (MRI) (intravenous contrast preferred) with a longest diameter ≥10 mm (except for lymph nodes, which must have a short axis ≥15 mm), and the lesion must be suitable for repeated accurate measurement. Lesions located in previously irradiated areas or that have undergone biopsy may serve as measurable target lesions if there is documented evidence of disease progression per RECIST v1.1. Brain lesions are not considered target lesions. 7. Have an estimated life expectancy ≥12 weeks as assessed by the investigator. 8. Demonstrate adequate bone marrow, hepatic, renal, and coagulation function based on laboratory tests performed within 7 days prior to first dose (hematology tests required within 3 days prior to first dose) \[supportive treatments, including transfusions, erythropoietin (EPO), granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), thrombopoietin (TPO), TPO receptor agonists (TPO-RA), and interleukins, are not permitted within 14 days prior to first dose\]: 1. Hematology: Absolute neutrophil count (NEUT) ≥1.5×10⁹/L; Platelet count (PLT) ≥100×10⁹/L; Hemoglobin (Hb) ≥90 g/L; 2. Hepatic function: Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤2.5×upper limit of normal (ULN); for participants with hepatic metastases, ALT and AST ≤5×ULN; Total bilirubin (TBIL) ≤1.5×ULN and direct bilirubin (DBIL) ≤1.5×ULN; 3. Renal function: Serum creatinine (Cr) ≤1.5×ULN, or calculated creatinine clearance ≥60 mL/min using the Cockcroft-Gault formula (see Appendix 4); Urinalysis indicating urine protein \<2+; for participants with urine protein ≥2+ on baseline urinalysis, a 24-hour urine collection should be performed with protein content \<1 g in 24 hours (if both testing methods are used, the 24-hour urine collection value will be used to determine eligibility); 4. Coagulation function: International normalized ratio (INR) ≤1.5; Activated partial thromboplastin time (aPTT) and prothrombin time (PT) ≤1.5×ULN. 9. Have a left ventricular ejection fraction (LVEF) ≥50% by echocardiography (ECHO) within 28 days prior to first study drug administration. 10. Hav