ing > 4 cm compared with 2% for tumours of 2-3 cm and 1% for those < 2 cm [8]. The growth rate also depends on the size. An endoscopic ultrasound (EUS) study of 226 pNETs in patients with MEN1 syndrome showed an average growth rate of 0.1 mm per year, with no size progression in tumours measuring < 10 mm but progression of 0.44 mm/year in larger tumours [11].Non-functioning sporadic tumours, which do not secrete hormones that cause clinical symptoms, are the most common type of pNETs and the focus of this review. The management of these tumours remains a clinical challenge and dilemma, largely because of uncertainty about their biology and factors related to malignant potential. Pancreatic surgery is complex and carries significant risk for complications including death, but taking a watch-and-wait approach risks development of metastases.There is consensus among experts and guidelines that NF-pNETs < 1 cm can be safely followed up, taking into account their small metastatic potential reported in the literature [5,12]. However, the European Neuroendocrine Tumour Society (ENETS) and North American Neuroendocrine Tumor Society (NANETS) guidelines are somewhat discrepant in their recommendation regarding when surgery should be performed for larger Pancreatic neuroendocrine tumours (pNETs) constitute up to 2% of pancreatic tumours and are detected with increasing frequency [1]. Most are sporadic, but they can develop as part of inherited syndromes, including multiple endocrine neoplasia 1 (MEN1), von Hippel-Lindau syndrome, and tuberous sclerosis [2][3][4]. These lesions are most commonly well-differentiated tumours with no hormonal activity, and their incidence increases with age [5]. The paucity of symptoms arising from their non-secreting nature is the primary reason they usually go undetected until they reach more advanced stages, compared with their functional counterparts. The overall 5-year survival in non-functional (NF)-pNETs is up to 43%, and median survival is 38 months. These survival metrics are much better than in pancreatic adenocarcinoma but still worse than in other gastrointestinal tumours such as colorectal cancer [6,7].Data indicate that the tumour size correlates with malignant potential, which in turn affects survival and mortality [8][9][10]. Bettini et al., using postoperative specimens, found that tumours measuring > 4 cm had significantly higher rates of microvascular invasion (26% vs. 13% for tumours < 2 cm) and of liver (4% vs. 0%) and nodal (20% vs. 13%) metastases [8]. The median antigen