Optimal preoperative treatment strategy for conversion surgery in unresectable locally advanced pancreatic cancer: A project study by the Japanese Society of Hepato-Biliary-Pancreatic Surgery.

718 Background: Conversion surgery (CS) for unresectable locally advanced pancreatic cancer (UR-LAPC) has been widely accepted when feasible. However, optimal preoperative treatment strategies remain unclear. To determine the most effective preoperative approach for UR-LAPC in the current treatment landscape, we conducted a project study in the Japanese Society of Hepato-Biliary-Pancreatic Surgery. Methods: We analyzed 465 UR-LAPC patients who underwent CS following chemotherapy with FOLFIRINOX (FFX), gemcitabine plus nab-paclitaxel (GnP), or modified regimens between 2015 and 2020 across 84 Japanese board-certified training institutions. Overall survival (OS) was the primary endpoint. We used the Kaplan-Meier method for estimating survival analyses, the Cox proportional hazards model for multivariate analyses, and Maximally Selected Rank Statistics to determine the optimal preoperative treatment duration. Results: Median OS was 43.8 months, with a 5-year survival rate of 37.2%. The optimal preoperative treatment duration was 6.1 months. Patients receiving >6 months of preoperative treatment (n=350) showed significantly better median OS and recurrence-free survival (RFS) compared to ≤6 months (n=115) (50.4 vs 29.7 months and 15.6 vs 9.1 months, respectively; both P<0.001 ). FFX-based regimens (n=116) showed better OS and RFS than GnP-based regimens (n=349) (65.0 vs 36.5 months and 19.3 vs 12.4 months, respectively; both P<0.01 ). Multivariate analysis identified preoperative treatment >6 months (HR 0.53, 95% CI 0.407-0.697, P<0.001 ) and initial FFX-based regimens (HR 0.63, 95% CI 0.464-0.843, P=0.002 ) as independent prognostic factors. Additional favorable factors included normal CA19-9 and CEA levels, PNI>45 before CS, adjuvant chemotherapy, R0 resection, and Evans grade III/IV. Conclusions: This large-scale retrospective study has demonstrated that preoperative treatment duration >6 months and the use of FFX-based regimens as initial treatment were associated with improved survival outcomes in UR-LAPC patients undergoing CS. These findings provide critical information for considering CS in UR-LAPC patients, especially in current clinical practice.