This is a Phase 1, first-in-human, open-label dose-escalation study to determine the maximum tolerated dose (MTD) and/or recommended Phase 2 dose (RP2D) and assess the DLT of JAB-3312. It is anticipated that approximately 24 subjects will be enrolled in the dose-escalation phase of the study. JAB-3312 will be administered orally once daily (QD) in 21-day treatment cycles.

Inclusion Criteria:

1. Subject must be ≥18 years-of-age at the time of signature of the informed consent form (ICF).
2. Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0 or 1.
3. Subjects with histologically or cytologically confirmed advanced solid tumors which have progressed despite standard therapy or for which no standard therapy exists.
4. Subjects with life expectancy ≥3 months.
5. Patients must have at least one measurable lesion as defined by RECIST v1.1.
6. Patients who have sufficient baseline organ function.

Exclusion Criteria:

1. Severe autoimmune disease (including immune-related adverse events of prior immune-oncology therapy) or autoimmune disorder that requires chronic systemic corticosteroid treatment at immunosuppressive doses (prednisone >10 mg/day or equivalent).
2. Known malignant central nervous system disease other than neurologically stable, treated brain metastases.
3. History or evidence of interstitial lung disease, radiation pneumonitis which required steroid treatment, or idiopathic pulmonary fibrosis, pleural or pericardial effusion that required intervention such as a drain.
4. 8. History of seropositive status for hepatitis B, hepatitis C and human immunodeficiency virus (HIV).
5. History or evidence of active infections (Grade ≥2).
6. History or evidence of significant inflammatory or vascular eye disorder.
7. History of an allogeneic bone marrow or solid organ transplant.
8. Use of systemic anti-cancer agent (except for anti-androgen therapy for prostate cancer) or investigational drug ≤28 days prior to the first dose of JAB-3312.
9. History of radiation therapy ≤28 days prior to the first dose of JAB-3312, or likely to require radiation therapy at any time until the 30 days after the last dose of JAB-3312.
10. History of transfusion of whole blood, red blood cell or platelet packets ≤2 weeks before the start of treatment.
11. Subjects experiencing unresolved Grade >1 toxicity before the start of treatment.