Clinical Efficacy of Neoadjuvant Chemotherapy with Gemcitabine plus S-1 for Resectable Pancreatic Ductal Adenocarcinoma Compared with Upfront Surgery.

BACKGROUND: The efficacy of neoadjuvant chemotherapy with gemcitabine plus S-1 (NAC-GS) in the prognosis of patients with resectable pancreatic ductal adenocarcinoma (PDAC) has been reported. NAC-GS is now assumed to be a standard regimen for resectable PDAC in Japan. However, the reason for this improvement in prognosis remains unclear. METHODS: In 2019, we introduced NAC-GS for resectable PDAC. From 2015 to 2021, 340 patients were diagnosed with resectable PDAC (anatomical and biological [carbohydrate antigen (CA) 19-9 < 500 U/mL]) and were divided according to the treatment period (upfront surgery [UPS] group, 2015-2019, n = 241; NAC-GS group, 2019-2021, n = 80). We used "intention-to-treat" analysis to compare the clinical outcomes of NAC-GS to those of UPS. RESULTS: Of the 80 patients with NAC-GS, 75 (93.8%) completed two cycles of NAC-GS, and the resection rate of the NAC-GS group was comparable to that of the UPS group (92.5 vs. 91.3%, P = 0.73). The R0 resection rate was significantly higher in the NAC-GS group than in the UPS group (91.3 vs. 82.6%, P = 0.04), even though the surgical burden was smaller. Progression-free survival tended to be better (hazard ratio [HR] = 0.70, P = 0.06), and overall survival was significantly better in the NAC-GS group than in the UPS group (HR 0.55, P = 0.02). CONCLUSIONS: NAC-GS provided improvements in microscopic invasion leading to a high R0 rate and smooth administration and completion of adjuvant therapy, which might lead to an improved prognosis in patients with resectable PDAC.