Phase II study of Neoadjuvant chemotherapy with Gemcitabine and S1 (GS therapy) for resectable pancreatic carcinoma (NAC GS2+2)

INTERVENTION: Neoadjuvant chemotherapy with gemcitabine and S1 CONDITION: resectable pancreatic cancer PRIMARY OUTCOME: True R0 resection rate; The rate of R0 resection with the normalized post‐operative tumor markers SECONDARY OUTCOME: Adverse effect, pathological effect, recurrence free survival, overall survival, patterns of recurrence, reduction rate and normalization rate for tumor marker INCLUSION CRITERIA: 1) invasive ductal carcinoma of the pancreas 2) no distant metastasis 3) R0/1 resectable 4) all adult who anticipate to undergo pancreatectomy 5) no prior therapy 6) written informed consent