A Phase 1, multiregional, open-label study of MST-168 in participants with target-driven advanced solid tumors.

The goal of this clinical trial is to evaluate the safety, tolerability, pharmacokinetics, immunogenicity, pharmacodynamic effects, and preliminary efficacy of MST-168 in participants with target-driven advanced solid tumors. MST-168 is an investigational ADC.

Inclusion Criteria:

• Participants are eligible to be included in the study only if all of the following criteria apply:

I1. Is capable of giving signed informed consent, including compliance with the requirements and restrictions listed in the ICF and in this protocol.

I2. Is at least 18 years of age at the time of signing the ICF.

I3. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.

I4. Life expectancy ≥ 12 weeks.

I5. Has adequate organ function.

I6. Pregnancy and Contraception: Female participants agree not to be pregnant or lactating from beginning of the study screening until 6 months after receiving the last treatment. Male participants with partners of childbearing potential and female participants of childbearing potential are willing and able to employ a highly effective method of birth control/contraception to prevent pregnancy from beginning of the study screening until 6 months after receiving the last treatment of MST-168.

I7. Has a pathologically documented advanced/unresectable or metastatic solid tumor that is refractory to or intolerable with standard treatment, or for which no standard treatment is available.

Exclusion Criteria:

• Participants are excluded from the study if any of the following criteria apply:

E1. Has untreated brain or CNS metastases or brain/CNS metastases that have progressed [e.g., evidence of new or enlarging brain metastasis or new neurologic symptoms attributable to brain/CNS metastases]. Participants with previously unstable brain or CNS metastases.

E2. Has a malignancy (except disease under study) that has progressed or required active treatment within the past 24 months except for basal cell or squamous cell carcinomas of the skin or in-situ carcinomas [e.g., breast, cervix, bladder] that have been resected with no evidence of metastatic disease.

E3. Has any history of prior allogenic or autologous bone marrow transplant or other solid organ transplant.

E4. Has known sensitivity to study intervention components or excipients.