The goal of this Phase I study is to evaluate the safety, tolerability, pharmacokinetics, and preliminary efficacy of QLS5308 monotherapy in participants with Advanced Solid Tumors. This study is divided into two phases: Phase Ia is the dose escalation phase, where dose escalation of QLS5308 conducted and RP2D is explored; In the Phase Ib tumor type expansion study stage, the primary objective is to evaluate the objective response rate (ORR) of QLS5308 with advanced solid tumors.

Inclusion Criteria:

• Has an eastern cooperative oncology group (ECOG) performance status of 0 to 1.
• Has adequate organ function.
• The expected survival period is ≥3 months.
• Based on the pathological report of the most recent biopsy or other pathological specimens, advanced or metastatic solid tumors confirmed by histology or cytology are not suitable for radical treatments such as surgery and radiotherapy.
• According to the RECIST v1.1 evaluation criteria, the participants had at least one radiologically measurable lesion.

Exclusion Criteria:

• Prior treatment with LIV1-targeting agents, ADCs with topoisomerase 1 inhibitor (TOP1i) payloads, or other TOP1i drugs.
• There was symptomatic central nervous system (CNS) metastasis, leptomeningeal metastasis or spinal cord compression caused by metastasis before the first use of the investigational product.
• Active, uncontrolled bacterial, fungal or viral infections.
• Participants with moderate to large amounts of uncontrolled pleural, pericardial, or peritoneal effusions before the first dose (those who remain stable for at least 2 weeks after drainage may be enrolled).
• Subjects with a history of a second malignant tumor other than the target indication within 3 years prior to signing the informed consent (excluding cured basal cell skin cancer, superficial bladder cancer, carcinoma in situ of the breast, papillary thyroid carcinoma, etc.).
• Prior to the first dose of the investigational product, all reversible toxicities from prior anti-tumor therapy (excluding alopecia and pigmentation) have not recovered to ≤ Grade 1 (as assessed by CTCAE v5.0), with the exception that peripheral neuropathy must have not recovered to ≤ Grade 2.
• Active autoimmune disease that requires systemic treatment or has the potential to recur.