Background: Platelets are believed to promote tumor growth and metastasis in several tumor types. The prognostic role of blood platelets in pancreatic ductal adenocarcinoma (PDAC) remains controversial, and the prognostic value of tumor-infiltrating platelets (TIPs) remains unknown.
Methods: A total of 303 patients who underwent curative pancreatectomy for PDAC were enrolled from two independent centers in China and divided into three cohorts. Paired preoperative blood samples and surgical specimens from all patients were analyzed. The correlations between patient outcomes and preoperative blood platelet counts and the presence of TIPs, respectively, were analyzed. TIPs were identified by immunohistochemical staining of CD42b. Prognostic accuracy was estimated by concordance index (C-index) and Akaike information criterion (AIC).
Results: TIPs, but not preoperative blood platelet counts, were associated with overall survival (OS; all P < 0.001) and recurrence-free survival (RFS; all P < 0.001) in the training, testing, and validation sets. Positive CD42b expression predicted poor postsurgical survival. Incorporation of TIPs improved the predictive accuracy of the 8th edition American Joint Committee on Cancer (AJCC) tumor-node-metastasis (TNM) staging system for OS in each of the three cohorts (C-index: 0.7164, 0.7569, and 0.7050, respectively; AIC: 472, 386, and 1019, respectively). The new predictor system was validated by incorporating TIPs with the 7th edition AJCC TNM staging system (C-index: 0.7052, 0.7623, and 0.7157; AIC: 476, 386, and 1015).
Conclusion: TIPs were an independent prognostic factor that could be incorporated into the AJCC TNM staging system to refine risk stratification and predict surgical outcomes of patients with PDAC.