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Other tumors

Primitive neuroectodermal tumor (PNET)

Reviewer: Deepali Jain, M.D. (see Reviewerspage)
Revised: 2 December 2012, last major update August 2012
Copyright: (c) 2001-2012, PathologyOutlines.com, Inc.


● Small round blue cell tumor with evidence of neuroectodermal differentiation; similar to tumors at other sites
● See also Kidney tumor chapter
● Mean 18 years (range 6 to 25 years, Am J Surg Pathol 2002;26:1040)
● Usually soft tissue or bone of children/young adults, rare in pancreas (1% of pancreas sarcomas)
● At all sites, 5 year survival is 50%

Case reports

● 17 year old boy (Mod Pathol 1994;7:200)
● 33 year old man with 18 cm tumor (World J Gastroenterol 2006;12:6070)
● 36 year old woman (Int J Clin Oncol 2012;17:399)
● 37 year old with 4 cm Ewing's sarcoma/PNET and multiple hepatic tumors (Intern Med 2009;48:329)

Gross description

● Tumors in head of pancreas, 3.5 to 9.0 cm

Micro description

● Sheets and lobules of small round cells with scant cytoplasm
● Prominent nuclear molding, frequent mitotic activity
● Often infiltrate into peripancreatic soft tissue
● Variable tumor necrosis
● Usually no rosettes

Micro images

Left: sheets of small round cells with rich fibrovascular stroma; middle: rudimentary rosette; right: diffusely CD99+

Site unspecified - left: sheets of uniform, small, round, blue cells. middle: Homer-Wright rosettes; right: atypical PNET with larger cells that often have a prominent nucleolus

Positive stains

● CD99 (O13/MIC2), cytokeratin, neuroendocrine markers (chromogranin, synaptophysin, NSE)

Negative stains

● Desmin

Molecular description

● t(11;22)(q24;q12)

Differential diagnosis

● Intraabdominal desmoplastic small round cell tumor: dense fibrous stroma, strong desmin staining, different t(11;22) than PNET
● Lymphoblastic lymphoma: CD99+ but TdT+ also
● Metastatic PNET to pancreas: see Clin Imaging 1997;21:23
● Neuroblastoma: younger patients, produce catecholamines, no t(11;22)
● Neuroendocrine carcinoma
● Pancreatic endocrine neoplasm: usually adults, slow growing; no molding, negative for neuroendocrine markers
● Pancreatoblastoma: usually age 10 or less, acinar formations, squamoid corpuscles, no t(11;22)
● Rhabdomyosarcoma
● Small cell carcinoma: higher mitotic rate, numerous karyorrhectic bodies, focal glandular differentiation, no t(11;22), usually elderly

End of Pancreas > Other tumors > Primitive neuroectodermal tumor (PNET)

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