Applications of a novel tumor-grading-metastasis staging system for pancreatic neuroendocrine tumors

The ability to stratify patients with pancreatic neuroendocrine tumors (p-NETs) into prognostic groups has been hindered by the absence of a commonly accepted staging system. Both the 7th tumor-node-metastasis (TNM) staging guidelines by the American Joint Committee on Cancer (AJCC) and the 2010 grading classifications by the World Health Organization (WHO) were validated to be unsatisfactory.We aim to evaluate the feasibility of combining the latest AJCC and WHO criteria to devise a novel tumor-grading-metastasis (TGM) staging system. We also sought to examine the stage-specific survival rates and the prognostic value of this new TGM system for p-NETs.Data of 120 patients with surgical resection and histopathological diagnosis of p-NETs from January 2004 to February 2014 in our institution were retrospectively collected and analyzed. Based on the AJCC and WHO criteria, we replaced the stage N0 and N1 with stage Ga (NET G1 and NET G2) and Gb (NET G3 and MANEC) respectively, without changes of the definition of T or M stage. The present novel TGM staging system was grouped as follows: stage I was defined as T1-2, Ga, M0; stage II as T3, Ga, M0 or as T1-3, Gb, M0; stage III as T4, Ga-b, M0 and stage IV as any T, M1.The new TGM staging system successfully distributed 55, 42, 12, and 11 eligible patients in stage I to IV, respectively. Differences of survival compared stage I with III and IV for patients with p-NETs were both statistically significant (P < 0.001), as well as those of stage II with III and IV (P < 0.001). Patients in stage I showed better a survival than those in stage II, whereas difference between stages III and IV was not notable (P = 0.001, P = 0.286, respectively). In multivariate models, when the TGM staging system was evaluated in place of the individual T, G, and M variables, this new criteria were proven to be an independent predictor of survival for surgically resected p-NETs (P < 0.05).Stratifying patients well, the current proposed TGM staging system was predictive for overall survival of p-NETs and could be more widely applied in clinical practice.