Study of SYN818 With Olaparib for the Treatment of Locally Advanced or Metastatic Solid Tumors

Inclusion Criteria: * Having signed the written Informed Consent Form (ICF); * Male or female aged ≥18 years; * Life expectancy ≥12 weeks; * Eastern Cooperative Oncology Group (ECOG) Performance Score 0 or 1; * Participant has a histologically confirmed diagnosis of advanced or metastatic solid tumor and has exhausted all standard-of-care treatment options, with documented BRCA mutations and/or homologous recombination repair deficiency (Part 1). * Participant has histologically or cytologically confirmed locally advanced or metastatic epithelial ovarian cancer or HER2-negative breast cancer, with documented BRCA mutations and/or homologous recombination repair deficiency (Part 2). * At least one measurable lesion according to Response Evaluation Criteria in Solid Tumors (RECIST) v1.1; * No serious hematological, cardiopulmonary, or liver or kidney diseases other than the primary disease; * Adequate organ function and bone marrow function. Exclusion Criteria: * Previous or current use of DNA Polymerase Theta (POLQ) inhibitors; * Current or previous other malignancy unless treated radically and with no evidence of recurrence or metastasis within the past 5 years; * Central nervous system (CNS) metastasis or meningeal metastasis with clinical symptoms, or other evidence indicating that CNS metastasis or meningeal metastasis has not been adequately controlled; * Patients with Myelodysplastic syndrome (MDS)/Acute myeloid leukemia (AML) or with features suggestive of MDS/AML; * Dysphagia or refractory nausea and vomiting, malabsorption, extracorporeal biliary shunts, or gastrointestinal disorders that affect drug absorption, e.g., Crohn's disease, ulcerative colitis, or short bowel syndrome, or other malabsorption conditions; * Treatment with an anti-cancer small molecule within 5 half-lives (t1/2), or 2 weeks, whichever is shorter; * History of use within 2 weeks prior to the first dose of the study treatment and need to use protocol-prohibited potent inhibitors or potent inducers of cytochrome P450 (CYP) 3A4/BCRP/P-gp during the study; * Serious systemic diseases or laboratory abnormalities or other conditions that, at the Investigator's discretion, will make it unsuitable for the patient to participate in this clinical trial.