A Clinical Study of 9MW2821 in Advanced Malignant Solid Tumors

Inclusion Criteria: * Competent to comprehend, sign, and date an independent ethics committee/institutional review board/research ethics board (IEC/IRB/REB) approved informed consent form. * Male or female subjects aged 18 to 80 years (including 18 and 80 years). * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. * Phase Ia：Histologically or cytologically confirmed advanced malignant solid tumors (except sarcoma). Phase Ib：Only local advanced or metastatic UC tumors. * Subjects must have received ICIs or GC/GP therapies in the previous treatment. * Subjects must submit tumor tissues for test. * Life expectancy of ≥ 3 months. * Subjects must have measurable disease according to RECIST (version 1.1). * Adequate organ functions. * Sexually active fertile subjects, and their partners, must agree to use methods of contraception during the study and at least 6 months after termination of study therapy. * Subjects are willing to follow study procedures. Exclusion Criteria: * Chemotherapy、radiotherapy or immunotherpy within 14 days prior to the first dose of study drug. * Preexisting treatment related toxicity Grade ≥ 2 (except alopecia). * Major surgery within 28 days prior to first dose of study drug. * History of uncontrolled diabetes mellitus. * Preexisting peripheral neuropathy Grade ≥ 2. * Received treatment of ADCs with MMAE payload. * Any live vaccines within 4 weeks before first dose of study drug or during the study. * Documented history of clinically significant cardiac or cerebrovascular diseases within 6 months prior to the first dose of study drug. * Other severe or uncontrolled disease, i.e. severe respiratory system disease, thromboembolic events, active bleeding or active infection. * Uncontrolled central nervous system metastases. * History of another malignancy within 3 years before the first dose of study drug. Subjects with curable malignancies are allowed. * History of autoimmune disease requiring systemic treatment within 2 years before the first dose of study drug. * Has ocular conditions that may increase the risk of corneal epithelium damage. * Known sensitivity to any of the ingredients of the investigational product; History of drug abuse or mental illness. * Any P-glycoprotein (P-gp) inducers/inhibitors or CYP3A4 inducers/inhibitors for high and medium effect within 14 days prior to the first dose of study drug. * Use of any investigational drug or device within 30 days prior to the first dose of study drug. * Conditions or situations which may put the subject at significant risk.