Impact of Surgical Resection After Induction Gemcitabine Plus S-1-Based Chemoradiotherapy in Patients with Locally Advanced Pancreatic Ductal Adenocarcinoma: A Focus on UR-LA Cases

<b>Background:</b> This study aimed to assess the safety and efficacy of gemcitabine plus S-1-based chemoradiotherapy (GS-CRT) among patients with locally advanced pancreatic ductal adenocarcinoma (PDAC), especially among those with unresectable locally advanced (UR-LA) cases. <b>Methods</b>: A total of 351 consecutive PDAC patients were enrolled and prognostic predictors of disease-specific survival (DSS) were identified. <b>Results:</b> The treatment completion rate was 98.9% and Grade 3 or higher adverse events occurred in 181 cases (51.6%). Among 319 re-evaluated patients, pancreatectomy was performed in 184 (57.7%). Based on resectability, the 5-year DSS rates for the entire cohort were 39.6% (R), 43.8% (BR-PV), 21.2% (BR-A) and 13.3% (UR-LA), while the predictors of DSS were performance status (PS), hemoglobin (Hb) level, celiac artery (CA) involvement of ≥180 degrees and JPS 8th T category. In the resected cases, the predictors of DSS were preoperative PS, preoperative CA19-9 level, preoperative JPS-T factor, degree of histological response and adjuvant chemotherapy. In UR-LA resected patients, preoperative prognostic nutritional index (PNI), absence of pathological venous invasion and adjuvant chemotherapy were predictors of DSS. <b>Conclusions:</b> Even though Grade 3 or higher adverse events were encountered in about half of the cases, they were uneventfully managed. Therefore, GS-CRT is safe and highly tolerable with potential to improve patients' prognosis. Preoperative PS, CA19-9 levels and histological response are important prognostic factors, as well as adjuvant therapy. In UR-LA patients, prognostic nutritional index (PNI) and adjuvant chemotherapy were important for curative intent surgery.