Resectable Pancreatic Adenocarcinomas following Neoadjuvant Chemotherapy with Gemcitabine Plus S-1: Two Case Reports of Opposite Oncological Outcomes.

[INTRODUCTION] Neoadjuvant gemcitabine plus S-1 (GS) therapy for resectable pancreatic cancer has been shown to prolong overall survival significantly compared with upfront surgery. Herein, we report two opposite cases of patients with resectable pancreatic cancer who underwent distal pancreatectomy after neoadjuvant GS therapy.

[CASE PRESENTATION] In Case 1, a 49-year-old female with a 12 mm tumor in the pancreatic body (cT1N0M0, cStage IA, union for international cancer control [UICC] 8th edition) underwent two courses of neoadjuvant GS therapy followed by an open distal pancreatectomy. Pathological examination revealed no residual cancer and the patient was diagnosed with a pathological complete response (pCR) without recurrence 31 months after surgery. However, in Case 2, a 74-year-old male with a 12 mm tumor in the pancreatic body (cT1N0M0, cStage IA, UICC 8th edition) also underwent two courses of neoadjuvant GS therapy, and then a laparoscopic distal pancreatectomy was performed. Pathological examination showed invasive pancreatic ductal adenocarcinoma with a 20 mm tumor. The tumor exhibited invasion into the lumen of the splenic vein and retroperitoneal tissue (ypT1N0M0, ypStage IA, UICC 8th edition). Adjuvant chemotherapy with S-1 was started, but 4 months postoperatively, a significant rise in serum CA19-9 levels was observed with multiple hepatic metastases and portal venous tumor thrombus. Gemcitabine plus nab-paclitaxel (GnP) therapy was started, however, the tumor progressed rapidly. The patient died 6 months after surgery.

[CONCLUSIONS] Neoadjuvant GS therapy is potentially expected to have a significant therapeutic effect as the pCR. Nevertheless, even after surgical resection, some patients still exhibit extremely poor prognosis. Therefore, it is necessary to clarify their clinical characteristics.