How are primitive neuroectodermal tumors (PNETs) classified?

Updated: Feb 07, 2019
  • Author: Carlo P Honrado, MD, FACS; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

Peripheral primitive neuroectodermal tumors (pPNETs) are also classified as part of the Ewing family of tumors (EFTs); peripheral primitive neuroectodermal tumors (pPNETs) and Ewing family of tumors (EFTs) are often referred to interchangeably in the literature. [3] Generally, Ewing family of tumors (EFTs) and peripheral primitive neuroectodermal tumors (pPNETs) represent different manifestations of the same tumor and have similar genetic alterations. Ewing sarcoma, however, is more common in bone, while peripheral primitive neuroectodermal tumors (pPNETs) are more common in soft tissues. Immunohistochemical and cytogenetic studies suggest that these tumors all have a common origin.

The following tumors are classified as peripheral primitive neuroectodermal tumors (pPNETs):

  • Ewing sarcoma (osseus and extraosseous) [4, 5]

  • Malignant peripheral primitive neuroectodermal tumors (pPNETs) or peripheral neuroepithelioma of bone and soft tissues

  • Askin tumor (peripheral neuroepithelioma of the thoracopulmonary region) [6]

  • Other less common tumors (eg, neuroectodermal tumor, ectomesenchymoma, peripheral medulloepithelioma) [7]

Stout first described PNETs in 1918, and these tumors were thought to arise directly from nerves. [8] The pathologic and cytogenetic understanding of these tumors has significantly advanced over the last 25 years. Based on molecular cytogenetic analysis, both EFTs and peripheral primitive neuroectodermal tumors (pPNETs) are known to share the same reciprocal translocations, most commonly between chromosomes 11 and 22. Further advances in immunohistochemical analyses have helped further distinguish PNETs and Ewing family of tumors (EFTs) from other small, round, poorly differentiated tumors, including rhabdomyosarcoma, neuroblastoma, and lymphoma. Peripheral primitive neuroectodermal tumors (pPNETs) often exhibit aggressive clinical behavior, with worse outcomes than other small, round cell tumors.


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