A Study to Evaluate the Safety,Tolerability, Pharmacokinetics and Clinical Activity of Mocertatug Rezetecan for Injection in Participants With Advanced Solid Tumors (BEHOLD-1)

Inclusion Criteria:

• Males or females aged 18 years or older (≥18 years).

• Participants with pathologically confirmed advanced solid tumor (who have failed orare intolerant to standard of care.

• PROC cohort

1. Histologically documented, advanced (metastatic and/or unresectable) high-gradeserous/endometrioid ovarian, primary peritoneal, or fallopian tube cancer.

2. Must have received or are intolerant to 1 but no more than 4 lines of priorsystemic therapy.

3. Platinum-resistant disease, defined as progression or relapse within 6 monthsafter the completion of platinum-based therapy.

4. Must have had prior bevacizumab , unless there is a documented contraindicationor intolerance.

5. Participants with known Folate receptor-α (FR-α) expressing tumors must havereceived mirvetuximab soravtansine if the regimen is locally available, unlessthere is a documented contraindication or intolerance.

Participants with known Breast cancer susceptibility gene (BRCA) mutated tumors should have received a Poly adenosine diphosphate-ribose polymerase (PARP) inhibitor if the regimen is locally available, unless there is a documented contraindication or intolerance.

• Endometrial cancer cohort

1. Histologically documented, advanced (metastatic and/or unresectable) orrecurrent endometrial cancer.

2. Must have received or are intolerant to 1 but no more than 4 lines of priorsystemic therapy.

3. Must have had prior platinum and PD(L)-1 inhibitor (in same regimen or inseparate regimens), if the regimen is locally available, unless there is adocumented contradiction or intolerance

4. All epithelial histologies are permitted including carcinosarcoma.

• Participants have at least one target lesion as assessed per the RECIST 1.1

• Tumor tissue from a newly obtained biopsy or archival tumor tissue is required forretrospective detection of B7 homolog 4 (B7-H4) expression by IHC in centrallaboratory and other biomarker analysis. Tissue from a newly obtained biopsy ispreferred. If a newly obtained biopsy is not feasible, archival tumor tissue within 2 years prior to the first dose of study drug is acceptable.

• Eastern Cooperative Oncology Group Performance Status (ECOG PS) score of 0 to 2 andno deterioration within 2 weeks before the first dose.

• Have a life expectancy of at least 12 weeks.

Exclusion Criteria:

• Have received any B7-H4-targeted therapy

• Have received any of cytotoxic chemotherapy drugs, anti-tumor traditional Chinesemedicines or other anti-tumor drugs within 28 days prior to the first dose of studydrug; or need to continue these drugs during the study.

• Have received locoregional radiation therapy within 2 weeks prior to the first doseof study drug; more than 30% of bone marrow irradiation or wide-field radiationtherapy within 4 weeks prior to the first dose of study treatment.

• Presence of pleural/abdominal effusion/ascites requiring clinical intervention;presence of pericardial effusion

• Major surgery within 28 days prior to the first dose of study treatment.

• Evidence of brain metastasis unless asymptomatic;

• Has inadequate bone marrow reserve or hepatic/renal functions .

• Mean Fridericia-corrected QT interval (QTcF) QTcF >450 msec or QTcF >480 msec forparticipants with bundle branch blocK;

• Evidence of current clinically significant arrhythmias or ECG abnormalities

• Left ventricular ejection fraction (LVEF) < 50%.

• Have severe, uncontrolled or active cardiovascular disorders, serious or poorlycontrolled hypertension, clinically significant bleeding symptoms or seriousarteriovenous thromboembolic events

• Has current active pneumonitis/ILD or any history of ILD, any history of pneumonitisrequiring steroids or immunomodulatory treatment within 90 days of plannedrandomization/enrollment or any history of drug-induced pneumonitis/ILD.Havereceived prior therapy with topoisomerase inhibitors or topoisomerase inhibitorAntibody-drug conjugate (ADCs)

• PROC

1. Primary platinum refractory disease defined as those who have progressed on orwithin 12 weeks of last dose of first line platinum therapy not permitted.

2. Non-epithelial carcinoma, clear-cell, mucinous, germ-cell, low-grade serous, orlow-grade endometrioid carcinoma not permitted.

• Endometrial cancer a. Mesenchymal tumors of the uterus (uterine sarcomas) notpermitted.