Case report of primitive neuroectodermal tumor with an unknown primary presenting with multiple lung metastasis

Ewing sarcoma or peripheral primitive neuroectodermal tumor (ES or pPNET) is a very aggressive cancer affecting children and young adults, with a five-year survival of 70–80% for localized disease and 30% for metastatic disease. ES can originate in any bone, but is most commonly reported in the lower extremities. To date, no cases of metastatic ES have been reported with an unknown primary in a patient over 45 years of age. We herein report the first documented case of metastatic ES to the lung with an unknown primary. Early diagnosis of rapidly invasive cancers such as ES is critical for effective treatment, which requires a multiple course combined chemotherapy regimen. The present case reports an atypical presentation of metastatic ES with bilateral involvement of the lungs and an unknown primary. We were able to definitively diagnose our patient with ES instead of other similar diseases such as small blue round cell tumor through immunohistochemical markers CD99 and NKX2.2, and began appropriate treatment.