Pathology of Primitive
Neuroectodermal Tumour of the Pancreas
Dr Sampurna Roy MD June 2016
Primitive neuroectodermal tumor (PNET - Small round blue cell tumour with evidence of neuroectodermal differentiation ) of the pancreas is an extremely rare tumour that usually occurs in children or young adults (mean age 18 years - age range between 6 to 25 years).
The tumour accounts for 1% of all sarcomas.
The tumour usually occurs in soft tissue or bone of children/young adults.
Peripheral primitive neuroectodermal tumours are characterized by chromosomal translocation t(11;22)(q24;q12) in almost 90% cases.
At all sites, 5 year survival is 50%
Gross features: Tumour is usually noted in the head of the pancreas (range between 3.0 to 9.0 cm in diameter).
Microscopic features: Sheets and lobules of small round cells with scant cytoplasm. There is prominent nuclear molding and prominent mitotic activity.
The tumour often infiltrate into peripancreatic soft tissue.
Tumour necrosis may be present.
Usually there are no rosettes.
Immunohistochemistry: The tumour stains positively with CD99, cytokeratin, neuroendocrine markers (chromogranin, synaptophysin, NSE) and is negative with desmin.
Visit: PNET of the soft tissue
Small cell carcinoma: Higher mitotic rate;numerous karyorrhectic bodies, focal glandular differentiation ; ; usually elderly population. t(11;22)
Pancreatoblastoma: Usually age 10 or less, acinar formations, squamoid corpuscles. t(11;22).
Neoplasms of the Endocrine Tumours : Usually adults, no molding, negative for neuroendocrine markers, slow growing tumours.
Neuroblastoma: Younger patients, produce catecholamines. t(11;22).
Lymphoblastic lymphoma (CD99+ but TdT+ also),
Metastatic PNET to pancreas: PNET of the soft tissue
Intraabdominal desmoplastic small round cell tumour : Dense fibrous stroma, strong desmin staining, different t(11;22) than PNET.
PNETs should be included in the differential diagnosis of poorly differentiated small round cell tumors of the pancreas.
They should not be confused with pancreatic endocrine tumors, which also demonstrate dual epithelial and neuroendocrine differentiation by immunohistochemistry.
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