This study is to evaluate the efficacy and safety of JAB-30355 in adult participants with advanced solid tumors harboring TP53 Y220C mutation.

This study consists of two parts: Dose Escalation Phase (Phase 1) and Dose Expansion Phase (Phase 2a). The primary objective of dose escalation is to evaluate the safety and tolerability, and to determine the MTD of JAB-30355 monotherapy administered in participants with advanced solid tumors harboring TP53 Y220C mutation. Dose expansion will further explore JAB-30355's clinical benefit and tolerability in selected dose levels.

Inclusion Criteria:

• Written informed consent.
• Participant must be ≥18 years of age at the time of signing the Informed Consent Form (ICF).
• ECOG performance status score of 0 or 1.
• Has been treated with at least one line of systemic therapy for that tumor type and stage.
• Have documentation of confirmed TP53 Y220C mutation.
• At least 1 measurable lesion per RECIST v1.1.
• Adequate hematological, renal and hepatic function and appropriate coagulation condition.
• Able to swallow and retain orally administered medication.

Exclusion Criteria:

• Active brain or spinal metastases or primary CNS tumor.
• Active infection requiring systemic treatment within 7 days.
• Active HBV or HCV.
• Any severe and/or uncontrolled medical conditions.
• LVEF ≤50% assessed by ECHO or MUGA.
• QTcF > 470 msec.