• Must have confirmed unresectable advanced/metastatic solid tumors (as outlined below) with disease progression on prior standard treatment, intolerance to or ineligibility for standard treatment, or no available standard treatment likely to improve the disease outcome in the judgment of the Investigator.

‣ Measurable disease per the RECIST v1.1

⁃ An Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1

⁃ Able to swallow oral medications.

∙ Dose Escalation(Part 1):

⁃ Ovarian cancer

⁃ Endometrial cancer

⁃ Gastric cancer or gastroesophageal junction cancer

⁃ Small cell lung cancer (SCLC)

⁃ Triple-negative breast cancer (human epidermal growth factor receptor 2 \[HER2\], estrogen receptor \[ER\], progesterone receptor negative)

⁃ ER/progesterone-receptor positive, HER2 negative breast cancer (must have progressed following treatment with a CDK4/6 inhibitor, and not suitable for endocrine therapy)

⁃ Other solid tumors with CCNE1 amplification as determined by NGS by local liquid or tissue biopsy.

∙ Dose Expansion (Part 2):

∙ a. Platinum resistant or refractory ovarian cancer (defined as recurrence ≤6 months after completing platinum-based regimen) with progression on at least 1 platinum containing therapy with CCNE1 amplification as determined by NGS by local liquid or tissue biopsy.

• Measurable disease per the RECIST v1.1

• An Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1

• Able to swallow oral medications.