This is an open-label, multicenter Phase II study of MHB036C combined with MHB039A in patients with advanced Breast Cancer or other advanced malignant solid tumors. The study was designed to evaluate the safety, tolerability, pharmacokinetics (PK), and efficacy of MHB036C and MHB039A combination therapy.

This phase II clinical trial of MHB036C and MHB039A combination therapy comprises two parts: a safety run-in phase and an indication expansion phase. The safety run-in phase includes a dose escalation part and an optional PK expansion part. The primary objectives are to evaluate the safety, tolerability, pharmacokinetics, and preliminary antitumor activity of MHB036C combined with MHB039A in patients with advanced solid tumors. The optional PK expansion part is allowed to enroll additional patients at any non-DLT dose levels that have completed DLT (dose-limiting toxicity) evaluation.

Based on the safety, PK, and preliminary efficacy data from the safety run-in phase, the sponsor will initiate the indication expansion phase at selected dose levels. This phase is an open-label, multicenter, multi-cohort study designed to further evaluate the efficacy and safety of MHB036C and MHB039A combination therapy in patients with advanced breast cancer and other 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 and ≤75 years, no restriction on gender.

3. Eastern Cooperative Oncology Group (ECOG) performance status of 0-1.

4. Estimated life expectancy ≥ 3 months.

5. Histologically or cytologically confirmed locally advanced or metastatic advanced solid tumors.

6. At least one measurable lesion per RECIST v1.1 criteria.

7. Adequate bone marrow reserve and organ function.

8. Eligible participants of childbearing potential (males and females) must agree to take highly reliable contraceptive measures with their partners during the study and within at least 12 weeks after the last dose.

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Exclusion Criteria:

1. History of ≥2 primary malignancies within 5 years prior to informed consent.
2. Received anti-tumor treatment within 4 weeks or within the 5 half-lives of the previous treatment (whichever is shorter) before dosing.
3. Medication of other unmarketed investigational drugs or therapies within 4 weeks before dosing.
4. Undergone major organ surgery (excluding biopsy) or significant trauma within 4 weeks before dosing or requiring elective surgery during the study.
5. Vaccinated with attenuated live vaccines within 4 weeks before dosing.
6. Treated with with systemic corticosteroids within 14 days before dosing.
7. Central nervous system metastasis.
8. Uncontrolled third-space effusion.
9. Serious cardiovascular or cerebrovascular diseases.
10. Severe lung disease affecting pulmonary function.
11. Active infection requiring systemic therapy.
12. Known hypersensitivity or delayed allergic reaction to the investigational product or its components.
13. Drug abuse or other medical/psychiatric condition that may interfere with study participation or results.
14. Known alcohol or drug dependence.
15. Pregnant or breastfeeding women, or individuals planning to conceive.