Well-Differentiated Neuroendocrine Tumor, Pancreas

Pancreatic Neuroendocrine TumorA well-circumscribed solid mass in the pancreas is typical of low-grade neuroendocrine tumors.

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Nested ArchitectureThe tumor cells show a nested pattern of growth. The individual tumor cells have uniform nuclei, small nucleoli, and lack prominent nuclear atypia, mitoses, or necrosis.
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Solid Growth PatternThe solid growth pattern and round monotonous nuclei support pancreatic neuroendocrine tumors, but immunohistochemistry is required to distinguish them from solid pseudopapillary tumors and acinar cell carcinomas.
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Chromogranin StainDiffuse positive staining is shown. Absence of reactivity for neuroendocrine markers (chromogranin/synaptophysin) should prompt reevaluation of the diagnosis.

TERMINOLOGY

Abbreviations

• Neuroendocrine tumor (NET)

Synonyms

• Pancreatic NET
• Pancreatic endocrine tumor
• Islet cell tumor

Definitions

• Low- to intermediate-grade NET of pancreas

ETIOLOGY/PATHOGENESIS

Syndromic

• Multiple endocrine neoplasia syndrome
• von Hippel-Lindau syndrome
• Tuberous sclerosis

Sporadic

• Majority of cases are nonsyndromic and sporadic

CLINICAL ISSUES

Presentation

• Epidemiology
image Peak incidence between 30-60 years
image No significant gender predilection
• Presenting symptoms
image Abdominal pain, jaundice
image Asymptomatic, detected by imaging
– Such incidentally detected pancreatic NETs are increasingly common
• Endocrine function
image Functioning tumors
– Insulinoma
– Glucagonoma
– Somatostatinoma
– Gastrinoma
– Vipomas
image Nonfunctional tumors
– More common than functional tumors

Treatment

• Surgical approaches
image Surgical resection remains mainstay of therapy for tumors confined to pancreas
image Enucleation is restricted to small tumors (typically < 2 cm)
• Options for tumors metastatic to liver
image Resection of primary and surgical debulking of metastatic tumor
image Long-acting somatostatin analogs (octreotide and lanreotide)
image Liver-directed therapy, including embolization, chemoembolization, radiofrequency ablation
image Novel agents, such as inhibitor of VEGF, inhibitor of tyrosine kinase, and mTOR pathway

Prognosis

• Outcome is variable
• Histological and immunohistochemical features help estimate risk of aggressive behavior
• Features associated with adverse outcome include
image Size > 2 cm
image Tumor necrosis
image Mitoses > 2/10 HPF
image Vascular invasion
image Perineural invasion
image High Ki-67 index
image CK19 positivity

IMAGING

CT Findings

• Solid, or less commonly, solid and cystic, well-circumscribed, enhancing lesion

MACROSCOPIC

General Features

• Solid, round to oval, well-circumscribed mass
• ∼ 5% of tumors are cystic
image Either multilocular or unicystic

Size

• Tumors < 0.5 cm are termed microadenomas

MICROSCOPIC

Histologic Features

• Monotonous population of round cells
• Nuclear chromatin is typically coarse with salt and pepper appearance
• Large nucleoli may be present
• Less common cytoplasmic variations include oncocytic, vacuolated lipid-rich variant, and rhabdoid

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Apr 20, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Well-Differentiated Neuroendocrine Tumor, Pancreas

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