This is a Phase 1, open-label, multicenter, single-arm, dose escalation study, designed to evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary antitumor activity of single-agent ASC61(an orally bioavailable small-molecule inhibitor of PD-L1) in subjects with advanced solid tumors for whom no standard therapy is available.

Except for the first starting dose of 200 mg once daily (QD), a traditional "3 + 3 design" will be followed for dose finding with dose escalation and/or de escalation as appropriate. Each subject in each dose cohort will use 2 dose schedules: single dose on Day 1 (D1), and repeated doses on daily basis for 28 days starting from Day 3. One treatment cycle is 28 days. Subjects will be sequentially enrolled in a dose-escalation design to receive ASC61 at initial dose of 200 mg QD. Subsequent doses of 200 mg twice a day (BID), 300 mg BID, 400 mg BID, 600 mg and 800 mg BID are planned.

Inclusion Criteria:

• Adults ≥ 18 years of age at the time of screening
• Histological or cytological diagnosis of advanced/metastatic solid tumor that is resistant to standard therapy or for which no standard therapy is available, regardless of cancer stage and previous experienced therapies
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
• At least one measurable lesion, as defined by RECIST 1.1

Exclusion Criteria:

• Known symptomatic brain metastases requiring steroids
• Known history of another primary solid tumor
• Subjects discontinued prior therapy with immune checkpoints due to toxicity if previously received therapy with this class of drugs
• Known history of idiopathic pulmonary fibrosis, drug-induced pneumonitis, or evidence of active pneumonia or pneumonitis
• Gastrointestinal disorders that might affect drug absorption