Study of MHB088C for Patients With Advanced Solid Malignant Tumors

Inclusion Criteria: * Agree to follow the experimental treatment plan and visit plan, join the group voluntarily, and sign a written informed consent form; * Age ≥ 18 years old when signing the informed consent form; * The Eastern Cooperative Oncology Group's physical status scoring standard (ECOG) is 0\~1; * The expected survival time is at least 3 months; * Eligible participants of childbearing potential must agree to take highly reliable contraceptive measures with their partners during the study and within at least 90 days after the last dose and agree not to retrieve, freeze or donate sperm or ova from screening to at least 3 months after the last dose of investigational drug; female participants of childbearing potential must have a negative results of blood pregnancy test before the first dose of investigational drug, and must be non-lactating. * Understand study requirements, willing and able to comply with study and follow-up procedures. Neoplasm-related criteria * Phase Ia: Histologically or cytologically confirmed unresectable advanced or metastatic malignant solid tumors, that is progressed or intolerant with standard of care (SOC), or for which no SOC regimens are available. * Phase Ib: Histologically or cytologically confirmed unresectable advanced or metastatic malignant solid tumors, that is relapsed or progressed following systemic treatment or no SOC is available; * Phase II: Histologically or cytologically documented unresectable advanced or metastatic SCLC and previous progressed during or after platinum-contained chemotherapy and immune-checkpoint inhibitors (ICIs). Exclusion Criteria: * Has more than 2 primary malignancies before signing of Informed Consent Form. * Has received anti-tumor treatment before the first dose of investigational product; Medication of traditional Chinese medicine before the first dose of investigational drug. * Medication of other unmarketed investigational drugs or therapies before the first dose of investigational drug. * Presence of unstable brain metastases and/or leptomeningeal carcinomatosis. * Has adverse reactions from previous anti-tumor treatment that have not recovered to ≤ CTCAE 5.0 Grade 1; * Has underwent major organ surgery or significant trauma before the first dose of investigational drug or requiring elective surgery during the study. * Has vaccinated with attenuated live vaccines before the first dose of investigational drug. * Has mucosal or internal bleeding for non-traumatic reason before the first dose of investigational drug. * Has received treatment with systemic corticosteroids or other immunosuppressive agents before the first dose of investigational drug. * Has pulmonary disease that severely impact pulmonary function. * Has history of non-infectious interstitial lung disease (ILD)/pneumonitis that required steroids, or current ILD/pneumonia, or suspected ILD/pneumonia that cannot be excluded by imaging examination at screening.