Study of TG6002 (VV TK-RR-FCU1) in Combination With 5-FC in Patients With Advanced Gastro-intestinal Tumors.

Inclusion Criteria: 1. Patient population: * Phase I part: patients with advanced GI carcinomas having failed and/or intolerant to standard therapeutic options. Patients must have been previously exposed to fluoropyrimidine-based chemotherapy. * Phase IIa part: patients with colorectal cancer and liver metastases having failed and/or intolerant to standard therapeutic options. Standard treatment consists of fluoropyrimidine-, oxaliplatin-, and irinotecan-based chemotherapy, possibly combined with an anti-VEGF and/or an anti-EGFR monoclonal antibody. In addition, the patient should not be candidate to a treatment with regorafenib. 2. Male or female aged ≥18 years. 3. a. Patient presenting with at least one measurable lesion according to RECIST 1.1 in Phase IIa part (optional in the Phase I part) b. Patient presenting with at least one biopsiable metastatic non target lesion (liver metastasis in the Phase IIa part) 4. Expected survival of at least 12 weeks 5. Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1 6. Absolute neutrophil count (ANC) ≥1000/mm3 7. Blood lymphocyte count ≥500/mm3 8. Hemoglobin (Hb) level ≥10 g/dL 9. Platelet count ≥100,000/mm3 10. Total bilirubin ≤1.5 x Upper Limit of Normal (ULN), except patients with Gilbert syndrome who must have a total bilirubin level of \<3.0 x ULN 11. AST, ALT, alkaline phosphatase ≤3 x ULN, unless if liver metastases are present (≤5 x ULN in that case) 12. Clearance for study participation and anti-hypertensive therapy suspension (see exclusion criterion 13) after cardiology consultation and cardiologic investigations including troponin T or I blood level, electrocardiogram (ECG) and cardiac echography (ECHO) 13. Negative blood pregnancy test for women of childbearing potential (WOCBP) 14. Highly effective method of contraception (i.e. methods with a failure rate of less than 1% per year) combined with a barrier method (e.g. condom) for male and female patients during TG6002 treatment period and for a minimum of 3 months following the last administration of TG6002 15. Signed written informed consent in accordance to ICH-GCP and national/local regulation Exclusion Criteria: 1. Previous irradiation of target tumor 2. MSI-High/dMMR colorectal cancer patients 3. Glomerular filtration rate \<60 mL/min/1.73m2 according to the Modification of Diet in Renal Diseases (MDRD) formula 4. Immunodeficiency due to underlying illness (e.g. HIV/AIDS) and/or immunosuppressant agent, including systemic corticosteroids at a dose \>10 mg/day of equivalent prednisolone taken for more than 4 weeks within 3 months prior to TG6002 treatment initiation 5. History of severe exfoliative skin condition (e.g. eczema or atopic dermatitis) requiring systemic therapy for more than 4 weeks within 2 years prior to TG6002 treatment initiation 6. Significant impairment of GI tract absorption, such as total gastrectomy, gastric mucosal atrophy, extensive intestinal resections or malabsorption disease 7. Symptomatic bacterial intestinal overgrowth consecutive to intestinal dysmotility, surgical resections (blind loops, ileo-cecal valve), or anatomical abnormalities 8. Inflammatory bowel disease (IBD) requiring treatment within the past 2 years prior to TG6002 administration and bowel sub-obstruction 9. Known deficiency in dihydropyrimidine dehydrogenase (DPD) 10. Known hypersensitivity to 5-FC or its excipients 11. Known hypersensitivity to eggs or gentamycin 12. Severe or unstable cardiac disease, including significant coronary artery disease (e.g. requiring angioplasty or stenting) within 12 months prior to TG6002 treatment initiation, unless well-controlled and on stable medical therapy for at least 6 months 13. Inability to withdraw anti-hypertensive therapy 24 hours prior to and up to 24 hours after TG6002 treatment AND/OR patients treated with 3 or more anti-hypertensive agents AND/OR patients with signs of advanced hypertensive disease, such as renal function impairment, left ventricular hypertrophy, hypertensive encephalitis or history of hemorrhagic stroke 14. Patients with other malignancies than the target disease in this trial except cutaneous basal cell carcinoma and in situ carcinoma of the uterine cervix, unless complete remission for at least 5 years prior to study entry and no additional therapy required during the study 15. Systemic anti-cancer therapy or resection surgery within 4 weeks prior to first administration of TG6002 16. Prior participation in another clinical study involving an IMP with last intake within 4 weeks prior to TG6002 treatment initiation 17. Other medical condition or laboratory abnormality that in the judgment of the investigator may increase the risk associated with study participation or may interfere with interpretation of study results 18. Prior gene therapy 19. Concurrent antiviral therapy active on vaccinia viruses (e.g. ribavirin) 20. Nursing (e.g. lactating) females 21. History of severe systemic reaction or side-effect after a smallpox vaccination, such as systemic vaccinia, eczema vaccinatum, encephalitis, myocarditis, pericarditis 22. Any psychological, familiar, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule 23. Patient unable or unwilling to comply with the protocol requirements 24. Severe uncontrolled coagulopathy OR anticoagulant medication for therapeutic purposes that cannot be discontinued prior to liver metastasis or other deep-seated tumor biopsies