A rare case of Ewing sarcoma with elevated plasma pro-gastrin-releasing peptide (proGRP) level

We studied a 17-year-old Japanese male with huge mass arising from the left third rib. The mass compressed the left lung and adhered to the pericardium, but the patient had no distant metastasis. He had a high level of plasma pro-gastrin-releasing peptide (proGRP). Histopathological examination of the bone biopsy specimen revealed small round cell tumor which was immunohistochemically positive for CD99 and vimentin. Gene analyses demonstrated EWSR1-FLI1 fusion, confirming the pathological diagnosis of Ewing sarcoma/primitive neuroectodermal tumor (ES/PNET). Several cycles of chemotherapy resulted in clinical good partial response, and plasma proGRP level at that time was normalized. Thereafter residual tumor was resected. Histopathological examination of the resected specimen showed no viable tumor cells, verifying the pathological complete response. High level of plasma proGRP before the chemotherapy and its normalization after the successful chemotherapy strongly suggest that ES/PNET in the present case was a proGRP producing tumor.