Nivolumab Adding on Gemcitabine/S-1 in Metastatic Pancreatic Cancer

This study assumes that to achieve significant therapeutic efficacy in advanced pancreatic cancer with immunotherapy, the immune system must remain relatively intact. Therefore, early use, low tumor load, adequate organ function, and slow growth of the tumor are the key points. Stage IV pancreatic adenocarcinoma patients with limited metastatic lesions and adequate organ function will be enrolled. Gemcitabine plus S-1 (GS) will be administered initially, and then CA 19-9 will be evaluated. Those fulfilling pre-defined criteria of CA 19-9 will receive nivolumab add-on therapy.