Historically termed “carcinoid” and “islet cell tumors,” pancreatic neuroendocrine tumors (PNETs) comprise a rare group of tumors that range from the spectrum of well-differentiated functional tumors to nonfunctional poorly differentiated carcinomas. This group of tumors often produces hormones resulting in clinically apparent symptoms. Derived from the islet cells of Langerhans, the first islet cell tumor was reported in 1902.1 Since then, 10 different categories of PNETs have been described, with all but one category being associated with a functional syndrome.
PNETs arise from pluripotent cells in the ductal and acinar epithelium of the pancreas (Table 49-1). While most PNETs occur infrequently, with one to five cases/million/year being newly diagnosed, autopsy reports reveal that these tumors may have an incidence of up to 1.5%, suggesting that many of these tumors may be asymptomatic.2,3 Optimal treatment for locoregional control of tumors includes surgical resection when feasible. Unfortunately, the malignant potential of these tumors cannot always be evaluated on histopathology alone, as the determination of malignancy requires evidence of local invasion or findings of metastases. With the exception of insulinomas, many PNETs may already have metastasized by the time of diagnosis.4,5 Malignant PNETs often have an indolent course, with a more favorable prognosis compared to that of other pancreatic tumors (i.e., pancreatic adenocarcinoma). These tumors are less sensitive to traditional chemotherapy; this raises the importance of an aggressive surgical approach, as well as the potential for adjunctive treatments including radiofrequency ablation, chemoembolization, and molecular targeted therapies.
Pancreatic Neuroendocrine Tumors
||Download (.pdf) TABLE 49-1
Pancreatic Neuroendocrine Tumors
|Islet Cells ||Active Secreted Hormone/Agent ||Tumor |
|Alpha ||Glucagon ||Glucagonoma |
|Beta ||Insulin ||Insulinoma |
|Delta ||Somatostatin ||Somatostatinoma |
|D ||Gastrin ||Gastrinoma |
|A to D ||VIP and other agents ||VIPoma |
| ||5HT ||Carcinoid |
| ||Melanocyte-stimulating hormone || |
| Interacinar cells || || |
|F ||Pancreatic Polypeptide ||PPoma |
|Enterochromaffin cells ||5HT ||Carcinoid |
PNETs comprise approximately 1.3% to 2.8% of all new pancreatic malignancies each year.5-7 Historically, the incidence of nonfunctioning PNETs was thought to be lower than functional PNETs. As a result of technologic improvements and increased use of cross-sectional abdominal imaging, this has been proven to not be the case. Recent reports have shown that only 15% to 30% of PNETS are functional; therefore, the overwhelming majority is now thought to be nonfunctional.3,5,8,9
Functional PNETs have the ability to produce a variety of hormones that result in well-defined clinical syndromes related to the particular secreted hormone. Excessive insulin secretion from an insulinoma can result in hypoglycemia; excessive gastrin production can result in diffuse peptic ulcer disease seen in patients with a gastrinoma. The presentation of diabetes and necrolytic migratory erythema (NME) is typical of that seen in patients with a glucagonoma. Somatostatinomas characteristically result in hyperglycemia, steatorrhea, and cholelithiasis.
PNETs are often seen in sporadic cases, ...