This is a first-in-human, open-label, multicenter Phase I study of MHB118C in patients with advanced solid tumors. The study was designed to evaluate the safety, tolerability, pharmacokinetics (PK), and preliminary efficacy of MHB118C monotherapy.

This first-in-human clinical trial of MHB118C comprises two parts: a dose escalation phase and indication expansion phase. The dose escalation phase is an open-label, multicenter study including dose escalation and PK expansion cohorts. The primary objectives are to evaluate the safety, tolerability, pharmacokinetics, and preliminary antitumor activity of MHB118C in patients with advanced solid tumors, and to determine the maximum tolerated dose (MTD). In this phase, additional patients may be enrolled in the PK expansion part at dose levels that have completed DLT (dose-limiting toxicity) evaluation.

Based on the safety, PK, and preliminary efficacy data from the completed DLT-evaluated dose levels, the sponsor will initiate the indication expansion phase. This phase is an open-label, multicenter, multi-cohort study designed to further evaluate the safety and efficacy of MHB118C monotherapy in patients with specific types of advanced solid tumors.

Inclusion Criteria:

1. Voluntarily agrees to participate in the study and signs the informed consent form.
2. Age ≥ 18 years, no restriction on gender.
3. Eastern Cooperative Oncology Group (ECOG) performance status of 0-1.
4. Estimated life expectancy ≥ 3 months.
5. Able to understand and comply with the study protocol and follow-up procedures.
6. Histologically or cytologically confirmed advanced solid tumors that are refractory to standard therapy, intolerant to standard therapy, or have no standard treatment options.
7. At least one measurable lesion per RECIST v1.1 criteria.
8. Adequate organ function.

Exclusion Criteria:

1. History of ≥2 primary malignancies within 5 years prior to informed consent.
2. Received chemotherapy within 3 weeks, radiotherapy within 4 weeks (2 weeks for palliative bone radiotherapy), or biologic, endocrine, or immunotherapy within 4 weeks before first study dose.
3. Brain metastases, leptomeningeal disease, brainstem metastases, or spinal cord compression.
4. Severe lung disease affecting pulmonary function.
5. Active systemic infection requiring treatment within 7 days before dosing.
6. Serious cardiovascular or cerebrovascular diseases
7. Uncontrolled third-space effusions not suitable for enrollment.
8. Known hypersensitivity or delayed allergic reaction to the investigational product or its components.
9. Drug abuse or other medical/psychiatric condition that may interfere with study participation or results.
10. Known alcohol or drug dependence.
11. Pregnant or breastfeeding women, or individuals planning to conceive.