Neuroendocrine Neoplasms of the Pancreas: A Multidisciplinary Approach

This is a well-differentiated neuroendocrine tumor of the pancreas (WD PNET), a G1 insulinoma in this case.

WD PNETs have an equal incidence in men and women; often affecting middle-aged adults. On histology they have a low-grade, generally monomorphic morphology with round nuclei, salt-and-pepper chromatin and clear to eosinophilic cytoplasm, containing secretory granules. Tumors can be functional or nonfunctional with nonfunctional tumors representing the majority. Insulinoma is the most common functional PNET. WD PNETs can have a trabecular, solid, pseudo-glandular or even a sarcomatoid growth pattern, though it is not uncommon to see more than one pattern in the same tumor. Being “endocrine in origin”, PNETs have traits similar to nerve cells and hormone-producing cells and are immunoreactive with synaptophysin, chromogranin and CD56. NESP-55, PDX-1, and less frequently, patchy CDX2 immunoreactivity is also reported in these tumors.

The majority of PNETs are considered sporadic and have no well-established, modifiable risk factor. In approximately 20% of cases a hereditary syndrome can be recognized. The main hereditary cancer syndromes associated with an increased risk for the development of PNETs are multiple endocrine neoplasia type 1 (MEN 1, autosomal dominant (AD), also known as Wermer Syndrome), Von Hippel-Lindau disease (VHL, AD) and neurofibromatosis type 1 (NF-1, AD). Genetic aberrations of DAXX and ATRX labeling are identified in a subset of WD PNETs.

Morphologic classification of NETs is based on the mitotic rate and proliferation index (assessed by Ki-67), as shown in table below (AJCC 8th edition/ CAP Pan. End. v4.0.0.1). Mitotic index is to be reported as the number of mitoses per 2 mm2, with at least 10 mm2 evaluated in the most mitotically active part of the tumor. When a discrepancy between the grades of the mitotic count and Ki-67 labeling index is observed, the higher grade, either that of the mitotic count or the Ki-67 labeling index, should be used.

Are G3 PNETs the same as poorly differentiated, pancreatic neuroendocrine carcinomas (NEC)?  No.

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