Macroscopic morphology for estimation of malignant potential in pancreatic neuroendocrine neoplasm.

Purpose: Pancreatic neuroendocrine neoplasm (Pan-NEN) representing approximately 1.3 % of pancreatic malignancy cases in incidence has been a so rare disease that it remains major problem to analyze the malignant potential. The aim of this study was to verify whether the macroscopic morphology of Pan-NEN, a novel pathological classification, contributes to malignant potential.

Methods: From a total of 86 patients with Pan-NEN, 41 surgical sections obtained from the primary site were classified by their morphology into a simple nodular (SN) group and a non-SN group. The non-SN group was further divided into three subtypes: simple nodular with extranodular growth (SNEG), confluent multinodular (CM), and infiltrative (IF). The clinicopathological features of the SN and the non-SN groups were retrospectively compared.

Results: Overall 5-year survival rates with and without surgical resection were 94 and 48 %, respectively. SN and non-SN types were identified in 21 and 20 patients, respectively. The non-SN group comprised 14 SNEG type, 2 CM type, and 4 IF type. Synchronous lymph node metastases (p = 0.009), synchronous liver metastases (p = 0.048), microinvasion to an adjacent organ (p < 0.001), vascular invasion (p = 0.023), and neural invasion (p = 0.019) were more significant in the non-SN group than in the SN group. As judged by WHO 2004 classification and TNM stages (AJCC and ENETS), non-SN type showed malignant trend (p < 0.05). Moreover, overall 5-year survival rates of SN and non-SN groups were 100 and 84.4 %, respectively (p = 0.048).

Conclusions: Non-SN tumors may have higher malignant potential than SN tumors.