Perineural and intraneural invasion in posttherapy pancreaticoduodenectomy specimens predicts poor prognosis in patients with pancreatic ductal adenocarcinoma

Perineural invasion (PNI) is one of the established prognostic factors in pancreatic ductal adenocarcinoma (PDAC). However, the prognostic significance of PNI in patients with PDAC who received neoadjuvant therapy and pancreaticoduodenectomy is not clear. In this study, we performed a detailed examination of neural invasion in pancreaticoduodenectomy specimens from 212 patients with PDAC who received neoadjuvant chemoradiation (treated group) and in 60 untreated patients at our institution between January 1999 and December 2007. The frequency of PNI was higher in the untreated group (80%, 48/60) than in the treated group (58%, 123/212). For the 123 treated cases that were positive for PNI, extratumoral PNI, intratumoral PNI, intrapancreatic PNI only, extrapancreatic PNI, and intraneural invasion were identified in 86 (69.9%), 37 (30.1%), 11 (8.9%), 112 (91.1%), and 35 cases (28.5%), respectively. The presence of PNI correlated with tumor size, margin status, lymph node metastasis, pathologic tumor, and American Joint Committee on Cancer stages in the treated group. Tumor involvement of nerves >0.8 mm correlated with higher frequency of positive margin compared with tumors with PNI involving nerves ≤0.8 mm but not with other clinicopathologic parameters and survival. In the treated group, the presence of PNI or intraneural invasion correlated significantly with shorter disease-free survival and overall survival compared with no PNI or PNI only, respectively. PNI was an independent prognostic factor for both disease-free survival and overall survival in multivariate analysis. Our results showed that PNI plays an important role in the progression of PDAC and in predicting prognosis in this group of patients.