A Study of MHB088C Injection Versus Treatment of Physician's Choice in Subjects With Relapsed Small Cell Lung Cancer

Prior treatment

• Diagnosis of other primary malignancies within 5 years prior to signing the informed consent form.
• Prior pathological diagnosis of combined SCLC, or any transformed non-small cell lung cancer or transformed SCLC.
• Receipt of chemotherapy within 4 weeks prior to the first administration of study drug, or receipt of radiotherapy, biologics, endocrine therapy, immunotherapy, or other anti-tumor therapy within 4 weeks prior to the first dose.
• Previous or ongoing treatment with topoisomerase I inhibitors, including antibody-drug conjugates (ADCs) containing topoisomerase I inhibitor payloads.
• Brain metastases (unless asymptomatic and stable for more than 4 weeks prior to randomization); presence of leptomeningeal metastases or brainstem metastases; spinal cord compression (identified via imaging, regardless of symptoms).
• Prior B7-H3-targeted therapy.
• Moderate-to-severe pulmonary disease significantly impairing lung function, including idiopathic pulmonary fibrosis, autoimmune/connective tissue disorders with lung involvement, or prior pneumonectomy.
• Serious infections within 4 weeks before the first dose, including but not limited to those requiring systemic antibiotic therapy, bacteremia, or severe pneumonia.
• Known hypersensitivity to investigational product components, analogues, or control drugs (e.g., topotecan, irinotecan, paclitaxel).

Other illness

• Has uncontrolled or significant cardiovascular disease.
• Has history of (non-infectious) interstitial lung disease (ILD)/pneumonitis that required corticosteroids, current ILD/pneumonitis, or suspected ILD/pneumonitis that cannot be ruled out by imaging at Screening.
• Moderate or severe pulmonary diseases severely affecting lung function.
• Active tuberculosis, autoimmune diseases not in clinical remission, other acquired or congenital immunodeficiency diseases, or history of allogeneic stem cell, bone marrow, or organ transplantation.

Other

• Participants who meet any of the following criteria will be disqualified from entering the study:
• Bone marrow metastasis.
• Clinically uncontrolled third-space effusion requiring intervention, including pleural or peritoneal effusions.
• Pregnant or lactating women, or women/men intending to conceive.

• Participants must meet all the following criteria to be eligible for randomization into the study:
• Voluntarily consent to participate in this study and sign the informed consent form.
• Adults ≥18 years, regardless of gender.
• ECOG performance status score of 0-1.
• Estimated survival time of more than 3 months.
• Capable of understanding trial requirements, willing and able to comply with trial and follow-up procedures.
• Has histologically or cytologically documented small cell lung cancer (SCLC).
• Extensive-stage SCLC with disease progression after at least two cycles of platinum-based and PD-1/L1 systemic therapy, with no more than two prior lines of therapy. Prior PD-1/L1 systemic therapy was allowed to use with or without platinum-based regimens.
• Agrees to provide pre-treatment tumor tissue samples for retrospective analysis of B7-H3 expression and other biomarkers.
• Has at least 1 measurable lesion according to RECIST v1.1 as assessed by the investigator.
• Sufficient bone marrow and organ function.