Neoadjuvant S-1 and Concurrent Radiotherapy for Borderline Resectable Pancreatic Cancer

Inclusion Criteria: * Cytologic or histologic proof of pancreatic ductal carcinoma or adenosquamous carcinoma is required prior to study entry. * Disease assessment by Multi Detector-row Computed Tomography (MDCT) scan within 2 weeks of study entry * Borderline resectable pancreatic cancer * No evidence of metastatic disease as determined by chest CT scan, and abdominal CT scan and laparoscopy. Paraaortic lymph node metastasis is considered as metastatic. * Age \>/=20 years old, \</=75 years old * Eastern Cooperative Oncology Group (ECOG) performance status 0-1 * No prior chemotherapy or radiotherapy for pancreatic cancer * A square 10 x 10 cm radiation field could encompass all pancreatic lesions and lymph node metastases * Adequate oral intake * Appropriate biliary drainage for obstructive jaundice * Lab Values: * hemoglobin concentration \>/= 9.0 g/dL * leukocyte count \>/= 3,000/mm3 * platelet count \>/= 100,000/mm3 * serum total bilirubin \</= 2.0 mg dL, or \</=3.0 mg/dL with biliary drainage * Aspartate Transaminase (AST) and Alanine Transaminase (ALT) \</= 100 U/L, or \</= 150 U/L with biliary drainage * serum albumin \>/= 3.0 g/dl * serum creatinine \</= 1.2 mg dL * Creatinine clearance \>/= 50 ml/min * Written informed consent Exclusion Criteria: * Tumor invasion to the alimentary tract determined by abdominal CT scan or endoscopic examination * Prior chemotherapy using fluoropyrimidine * Prior radiation therapy to the abdomen * Watery diarrhea * Concurrent phenytoin, warfarin potassium, or flucytosine treatment * Presence of contrast medium allergy * Pulmonary fibrosis or interstitial pneumonia * Pleural effusion or ascites * Active infection * Uncontrolled diabetes mellitus (FBS \>/= 200mg/dL or HbA1c \>/= 10.0) * Active concomitant malignancy * Active gastroduodenal ulcer * Severe complications such as cardiac or renal disease * Regular administration of systemic corticosteroid * Psychiatric disorder * History of drug hypersensitivity * Pregnant and lactating women and women of childbearing age who were not using effective contraception