• Histologic or cytologic evidence of gastric/gastroesophageal junction carcinoma, classified as diffuse type, poorly cohesive, signet ring cell, or mixed type. Patients with known pathogenic CDH1 and/or RHOA mutations will be allowed regardless of histology.

• Prior therapy with at least one line of therapy for unresectable/metastatic disease, which must include platinum and fluoropyrimidine.

• ECOG performance status of 0 or 1

• Age ≥ 18 years

• Adequate organ function, defined by the following laboratory parameters:

• a. Adequate hematologic function, including hemoglobin \[Hb\] ≥ 9.0 g/dL; platelets ≥ 100,000/mm3; and absolute neutrophil count \[ANC\] ≥ 1500/mm3. If a red blood cell transfusion or erythropoiesis-stimulating agent has been administered the Hb must remain stable and ≥ 9 g/dL for at least 1 week prior to first dose of study intervention.

• (i) Subjects with Hgb ≥ 8.5 g/dL and \<9.0 g/dL are eligible if there is no history of significant cardiovascular risk features as per the investigator (i.e., prior myocardial infarction) b. Adequate hepatic function: (i) total bilirubin ≤ 1.5 × upper limit of normal \[ULN\] for the institution; patients with Gilbert syndrome may enroll if total bilirubin is \< 3.0 mg/dL (51 μmol/L); (ii) alanine aminotransferase (ALT) and aspartate aminotransferase (AST)

• ≤ 2.5 × ULN (or \< 5 x ULN in patients with liver metastases). c. Adequate renal function with creatinine clearance rate of ≥ 50 mL/min, as calculated by the Cockcroft-Gault formula d. International normalized ratio (INR) ≤ 1.5 and partial thromboplastin time (PTT) ≤ 1.5 x ULN in the absence of anticoagulation or therapeutic levels in the presence of anticoagulation.

• e. Albumin ≥ 3.0 g/dL (451 μmol/L). f. Creatine phosphokinase (CPK) ≤ 2.5 x ULN. g. Adequate cardiac function with left ventricular ejection fraction ≥ 55% by echocardiography (ECHO) or multiple-gated acquisition (MUGA) scan.

• Disease that can be evaluated radiographically, which can be measurable disease or non-measurable disease per RECIST 1.1. All radiology studies must be performed within 28 days prior to start of study-directed therapy.

• Tumor that is amenable to fresh biopsy, which may include malignant ascites that is amenable for paracentesis.

• Baseline QTc interval \< 460 ms for females and ≤ 450 ms for males (average of triplicate readings) using Fredericia's QT correction formula. NOTE: This criterion does not apply to subjects with a right or left bundle branch block.

• Adequate recovery from toxicities related to prior treatments to at least Grade 1 by CTCAE v 5.0. Exceptions include alopecia and peripheral neuropathy grade ≤ 2. Subjects with other toxicities that are stable on supportive therapy may be allowed to participate with prior approval from the principal investigator.

⁃ The effects of the study drugs on the developing human fetus are unknown. For this reason, women of child-bearing potential and men must agree to use adequate contraception (see Section 7.6 for Contraception Guidance) prior to study entry and for the duration of study participation. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately. Men treated or enrolled on this protocol must also agree to use adequate contraception prior to the study, for the duration of study participation, and 3 months after the last dose of the study drug.

⁃ Ability to understand and the willingness to sign a written informed consent document.