Survival Impact of Pathological Residual Patterns for Pancreatic Ductal Adenocarcinoma After Neoadjuvant Therapy

BACKGROUND: With increasing use of neoadjuvant therapy (NAT) for pancreatic ductal adenocarcinoma (PDAC), accurate pathological response system is essential. Although the College of American Pathologists (CAP) grading is widely used, its prognostic utility remains limited. METHODS: This retrospective study included 206 patients with resectable or borderline resectable PDAC who underwent pancreatectomy following NAT. Pathological residual patterns were morphologically classified into three categories-type I (concentric distribution of residual tumor without any surrounding lesions), type II (concentric distribution with surrounding lesions), type III (residual multinodular lesions)-with types I, II grouped as the concentric type, and types III as the multinodular type. RESULTS: The concentric type had significantly longer median overall survival (OS: 133 vs. 32 months) and disease-free survival (DFS: 32 vs. 18 months) compared with the multinodular type (both p < 0.001). Residual patterns was an independent prognostic factor for OS (HR: 2.62, p = 0.017), whereas CAP grading was not (p = 0.142). Residual patterns also provided superior prognostic discrimination, with higher Harrell's C-index for OS than CAP grading (0.711 vs. 0.595; p = 0.047). CONCLUSION: Pathological residual patterns may serve as a practical prognostic indicator after NAT.