A Study With NKT3964 for Adults With Advanced/Metastatic Solid Tumors

Inclusion Criteria:

\- Must have a pathologically confirmed, advanced and unresectable or metastatic solid tumor listed below with documented disease progression on last standard treatment.

For Part 1 only: Patients must be refractory to, or intolerant of existing therapy(ies) known to provide clinical benefit for their condition.

Part 1 Dose Escalation and Food Effect Sub-study:

1. Ovarian cancer 2. Endometrial cancer (only 'endometrioid' subtype requires CCNE1 amplification) 3. Gastric, gastroesophageal junction (GEJ) or esophageal adenocarcinoma with CCNE1 amplification 4. Small cell lung cancer (SCLC) 5. Triple-negative breast cancer (TNBC; HER2, estrogen receptor and progesterone receptor negative) 6. HR+ (includes estrogen-receptor or progesterone-receptor) and HER2- breast cancer (must have progressed following treatment with a CDK4/6 inhibitor, and is not suitable for endocrine therapy \[ET\]) 7. Other solid tumors with CCNE1 amplification

Part 2 Dose Expansion:

Part 2A: HR+ and HER2- breast cancer that is locally advanced and unresectable (Stage III) or metastatic (Stage IV); previously treated with ≥1 line of SOC including CDK4/6 inhibitor plus ET and not suitable for further ET. Subjects must have progressed after receiving therapy for ≥3 months in the metastatic setting or for ≥6 months in the adjuvant setting. Subjects must have received ≤2 lines of systemic cytotoxic therapy (chemotherapy or cytotoxic antibody drug conjugate) in the metastatic setting.

Part 2B: Advanced platinum-based chemotherapy- resistant or refractory epithelial ovarian/fallopian/primary peritoneal carcinoma or clear cell ovarian cancer (defined as recurrence ≤6 months after completing platinum-based regimen) with progression on at least one platinum containing therapy and previously treated with ≤4 prior lines of systemic therapy administered for advanced/metastatic disease and with CCNE1 amplification.

Part 2C: Advanced unresectable or metastatic gastric, GEJ or esophageal adenocarcinoma with progression on at least one systemic therapy and previously treated with ≤3 prior lines of systemic therapy administered for advanced/metastatic disease, with CCNE1 amplification as determined by NGS by local liquid or tissue test.

Part 2D: Advanced endometrial adenocarcinoma or uterine papillary serous carcinoma previously treated with ≤4 prior lines of systemic therapy administered for advanced/metastatic disease with CCNE1 amplification.