D. Primitive neuroectodermal tumor (PNET)—extraskeletal Ewing's sarcoma
PNET is the more common designation for this tumor, which in the past was also coded under the names of extraskeletal Ewing’s sarcoma, Askin tumor, or neuroepithelioma.
The tumor is more common in younger patients, although it can occur in older individuals as well.
The tumor commonly expresses CD99 (HBA71, or the MIC2 gene product) as well as other nonspecific markers such as neuron-specific enolase (NSE). More importantly, these tumors are negative for muscle and epithelial markers. Chromosomal translocations t(11;22)(q24;q12) and t(21;22)(q22;1q12) have been demonstrated in these tumors.
The treatment of choice for these tumors is chemotherapy; however, the prognosis in general is not good.