The research study is being conducted to study whether performing injections of a new treatment, called RP2, directly into stomach and esophagus tumors along with standard chemotherapy (called FLOT) is safe and whether it does a better job of killing cancer before surgery compared to chemotherapy alone.

This is a single-arm, phase II study using a Simon two-stage optimal design with a 6 patient safety run-in evaluating the addition of intra-tumoral injections of RP2 to standard of care perioperative FLOT for patients with stage II or higher, non-metastatic esophageal, gastroesophageal junction (GEJ), or gastric adenocarcinoma. We hypothesize that the addition of RP2 to perioperative FLOT will be safe and will significantly improve pathologic complete response (pCR) rate compared to the historical weighted average of 12% observed with perioperative FLOT in the ESOPEC trial, MATTERHORN trial, and FLOT4 trial.

Inclusion Criteria:

• Patients must have histologically confirmed and clinically staged T2 or higher or node positive, non-metastatic esophageal, gastroesophageal junction, or gastric adenocarcinoma.

• Patients must have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 - 1.

• Patents must be deemed a surgical candidate by a thoracic surgeon, surgical oncologist, or surgeon who is qualified to perform the appropriate surgical procedure based on patient's primary tumor site.

• Patients must have normal organ and bone marrow function, as defined below, less than or equal to 14 days prior to the initiation of study therapy:

  • Absolute neutrophil count (ANC) ≥ 1,500/microliter
  • Platelets ≥100,000/microliter
  • Total bilirubin ≤ the institutional upper limit of normal (ULN).
  • AST and ALT ≤ 2.5 times the institutional ULN
  • Serum creatinine ≤ 1.5 times the institutional ULN
  • Hemoglobin ≥ 9 g/dL

Exclusion Criteria

• Has received prior chemotherapy, radiation therapy, or immunotherapy (anti-programmed cell death protein-1 (PD-1), anti-programmed death ligand-1 (PD-L1), or anti-cytotoxic T-lymphocyte associated protein 4 (CTLA-4) for the current malignancy.

• Per the investigator, has contraindications to receiving chemotherapy with FLOT.

• Per the sub-investigator (gastroenterologist) responsible for intra-tumoral injections or the investigator, patient has contraindications to repeated upper endoscopy for intra-tumoral injections. These could include medical conditions that would, per the judgment of the sub-investigator or investigator, inappropriately increase the risk of upper endoscopy.

• Conditions in which anticoagulant therapies cannot be safely stopped in the periprocedural period or patients on warfarin with a target international normalized ratio (INR) ≥ 2.5 that cannot be temporarily reversed to INR ≤ 1.7.

• Active significant herpetic infections or prior complications of Herpes simplex virus-1 (HSV-1) infection (e.g., herpetic keratitis or encephalitis) or requires intermittent or chronic use of systemic (oral or intravenous [IV]) antivirals with known antiherpetic activity (e.g., acyclovir). Note: Patients with sporadic cold sores may be enrolled as long as no active cold sores are present at the time of first dose of study treatment.

• Has received a live vaccine within 30 days prior to the first dose of study drug. Examples of live vaccines include, but are not limited to: measles, mumps, rubella, varicella/zoster (chicken pox), yellow fever, rabies, Bacille Calmette-Guérin (BCG), and typhoid vaccine. Note: Seasonal influenza vaccines for injection are generally killed virus vaccines and are allowed, however, intranasal influenza vaccines (e.g., FluMist®) are live attenuated vaccines and are not allowed. Available COVID-19 vaccines do not contain live virus and are allowed.

• Has a condition requiring systemic treatment with corticosteroids (>10mg/day prednisone equivalents) or other immunosuppressive medications within 14 days of first study treatment administration.

  • Inhaled or topical steroids and adrenal replacement doses ≤ 10mg/day of prednisone equivalents are permitted.

• Prior organ transplantation including allogeneic stem-cell transplantation.

• Has a previous or concurrent malignancy. Exceptions include:

  • Non-melanoma skin cancer, in situ cervical cancer, superficial bladder cancer, or breast cancer in situ OR
  • Prior malignancy has been completely excised or removed and patient has been continuously disease free for > 5-years

• Has a positive test result for hepatitis B virus surface antigen (HBsAg) or hepatitis C virus ribonucleic acid (HCV RNA) indicating acute or chronic infection with hepatitis B or hepatitis C. Testing will be performed as part of screening on the study.

  • Patients with a known history of hepatitis B or hepatitis C that have been effectively treated (with negative HBsAg and HCV RNA) will be eligible for enrollment on this criterion.

• Has a known history of human immunodeficiency virus (HIV) with detectable viral load. HIV testing will not be performed as part of screening for the study.

  • Patients with known HIV infection with an undetectable viral load and who are on a stable highly active antiviral regimen per the investigator's assessment will eligible to enroll.

• Has a psychiatric illness, substance use, or other social conditions that, in the judgment of the investigator, would limit compliance with study requirements.

Individual participant data that underlie the results reported in the clinical trial publication, after deidentification (text, tables, figures, and appendices).

Beginning 3 months following clinical trial publication. No end date.

To achieve aims in an approved proposal. Proposals should be directed to corresponding author on the clinical trial publication.