* Inclusion Criteria:
\- Patients who meet all of the following criteria will be eligible for this study. Besides, CTCAE v5.0 will be used to determine the grade of adverse events in this study.
1. Patients with unresectable pancreatic cancer who are histologically or cytologically diagnosed as adenocarcinoma based on the 7th edition of the Pancreatic Cancer Treatment Protocol and meet the following criteria.
Patients who have not received any anticancer therapy (radiation therapy, chemotherapy, immunotherapy, surgery, or investigational therapy) for this disease.
2. Patients who are between 20 and 79 years of age at the time of consent.
3. Patients with at least one measurable lesion based on RECIST ver 1.1 in the primary pancreatic lesion confirmed by contrast-enhanced CT at the screening.
4. Patients who are expected to survive for at least 12 weeks after the start of treatment.
5. Patients who can understand the contents of this study and can give written consent.
6. Patients with ECOG PS (Eastern Cooperative Oncology Group Performance Status) of 0 or 1
7. Patients who meet the following criteria in blood tests within 7 days before enrollment and whose organ functions are preserved (if blood transfusion is used, tests must be performed at intervals of at least 2 weeks afterward)
* Total bilirubin ≤ upper limit of institutional standard (ULN) x 1.5 (less than or equal to 3.0 mg/dL for patients undergoing ERBD or PTBD)
* AST (GOT) and ALT (GPT) ≦ ULN × 3 (In the case of abnormal liver function due to malignancy, ≤ ULN × 5)
* Creatinine ≤ 1.5 mg/dL or
* Creatinine clearance ≥ 60ml/min If creatinine clearance is not measured, the estimated value should be used.
* White blood cell count ≥ 3,500/mm3, ≤ 12,000/mm3
* Neutrophils ≥ 1,500/mm3
* Platelet count ≥ 100,000/mm3
* Hemoglobin ≥ 9.0g/dL
* Prothrombin activity level ≥ 70%
8. Outpatients who can go to the hospital.
9. Patients who can swallow or continue to take oral medications.
10. For women of childbearing potential, patients who can use contraception for at least 30 days before the start of study treatment, during the study period, and for at least 2 years after the end of treatment.
11. Patients who can undergo biopsy from pancreatic cancer ①within 28 days before the start of the study treatment and ② 8 weeks after the start of the study treatment (Day 57: acceptable range: ±7 days)
* Exclusion Criteria:
1. Patients with any of the following complications Patients with poorly controlled heart disease (congestive heart failure, myocardial infarction, or unstable angina within 1 year before enrollment, arrhythmia requiring treatment, etc.) Poorly controlled diabetes or hypertension Active autoimmune disease requiring systemic administration of steroids or immunosuppression therapy Interstitial pneumonia or pulmonary fibrosis (patients with current grade 2 or higher)
2. Patients who have received other clinical trial drugs or products (excluding existing chemotherapeutic agents and placebo drugs) within 4 weeks before enrolment.
3. Patients with confirmed brain metastasis (confirmed by head CT or MRI if the patient has symptoms of brain metastasis)
4. Patients with ascites or pleural effusion requiring drainage.
5. Patients who fall under any of the following HBs antigen positive HCV antibody positive and HCV-RNA positive HIV antibody positive
6. Patients with Grade 2 or higher peripheral sensory or motor neuropathy
7. Patients with multiple cancers (multiple cancers are defined as simultaneous multiple cancers and metachronous multiple cancers with disease-free survival of 5 years or less. lesions equivalent to carcinoma in situ or intramucosal carcinoma that are considered curable by local treatment are not included in multiple cancers)
8. Patients who have undergone surgery (excluding diagnostic biopsy and review laparoscopy) within 4 weeks before enrollment.
9. Patients with bleeding disorders or coagulation disorders that preclude the safe biopsy under EUS (e.g., significant intratumoral bleeding, coagulation disorders, history of bleeding disorders, or complications).
10. Patients with a history of allergy to the trial drug, combination chemotherapy, its additives, or vitamin A products.
11. Patients requiring anticoagulant medication.
12. Patients with cerebral infarction, pulmonary infarction, other arterial or venous thrombosis or its sequelae with clinical symptoms.
13. Patients with gastrointestinal disorders that may affect the absorption of the investigational drug.
14. Female patients who are pregnant or breastfeeding (unless breastfeeding is discontinued and not resumed).
15. Male patients whose sex partner is a woman who wishes to become pregnant.
16. Patients with vitamin A overload.
17. Patients receiving vitamin A preparations or regularly using vitamin A-containing supplements (patients can be enrolled if the administration is discontinued at the time of obtaining consent).
18. Other patients deemed inappropriate by the investigator or sub-investigator.
