A Study of a Mutant-Selective Inhibitor, CGT6297, in Patients With Advanced Solid Tumors Harboring PIK3CA Mutations

Inclusion Criteria: 1. Histologically confirmed advanced solid tumor harboring oncogenic PIK3CA mutations in blood and/or tumor: 1. Phase 1b Cohort 1, participants must have PIK3CA endometrial cancer 2. Phase 1b Cohort 2, participants must have HR-positive/HER2-negative or HER2-low breast cancer (immunohistochemistry \[IHC\] and in-situ hybridization results must meet ASCO-College of American Pathology guidelines for breast cancer or criteria) 3. Phase 1b Cohort 3 will allow all solid tumors that do not meet criteria for Phase 1b Cohorts 1 or 2, including head and neck cancers, other gynecological cancers, colorectal cancers harboring PIK3CA mutations 2. Meet prior treatment requirement of: 1. Phase 1a: previously treated with and refractory to or intolerant of existing therapy(ies) known to provide clinical benefit for their condition. 2. Phase 1b: previously treated with or considered not appropriate for SOC first-line treatment for their condition 3. Have at least one measurable lesion according to RECIST v1.1. 4. Eastern Cooperative Oncology Group (ECOG) Performance Status 0 to 1 5. Have clinically acceptable local laboratory screening results (clinical chemistry and hematology) within certain limits 6. Resolution of acute toxicities from prior anticancer therapy to ≤Grade 1 (or baseline), including resolution of clinically significant laboratory abnormalities (other than parameters specified in screening testing as outlined below), as determined by the National Cancer Institute-Common Terminology Criteria for Adverse Events (NCICTCAE) v5.0. 7. Have an ejection fraction ≥50% Exclusion Criteria: 1. Received small molecule chemotherapy or anticancer therapies or radiotherapy within certain timeframes before first dose of study drug. 2. Major surgeries (eg, abdominal laparotomy) within 4 weeks of the first dose of study drug 3. Treatment with radiotherapy ≤2 weeks before the first dose of study drug. 4. Clinically significant cardiac disease 5. Ongoing or planned long-term (≥4 consecutive weeks) treatment with glucocorticoid steroids at greater than physiologic dosing (defined as equivalent to \>20 mg/day prednisone) 6. Diagnosis of diabetes mellitus type 1 or uncontrolled diabetes mellitus type 2 (defined as fasting glucose ≥140 mg/dL and HbA1c ≥7.0%; antihyperglycemic medical management permitted with the exception of insulin) 7. Previous molecular testing (NGS or PCR) showed tumor with the following mutations: mutations/deletions in PTEN or activating mutations in AKT, HRAS/KRAS/NRAS, EGFR, and BRAF