We recently encountered a very rare case of periosteal Ewing's sarcoma (PES), which was treated by surgery followed by photodynamic therapy using acridine orange with radiodynamic therapy. No more than 15 cases of PES have been reported previously in literature. In our case, MRI revealed the tumor to be localized on the cortical surface of the proximal humerus. Histopathological examination of biopsy specimens revealed a small round cell sarcoma suggestive of Ewing's sarcoma or PNET, and immunohistochemistry showed positive staining for MIC2. Although fusion genes EWS-FLI1 and EWS-ERG were undetectable, PES was still considered to be the most likely diagnosis. Therefore, we administered preoperative chemotherapy, as a result of which the tumor shrank to 48% of its original volume. With a view to preserve excellent shoulder and upper limb function, we attempted intralesional tumor resection supported by photodynamic therapy using acridine orange with radiodynamic therapy. After surgery followed by postoperative chemotherapy, the patient has, until the time of writing, had no local tumor recurrence and no evidence of metastatic disease, and can move his shoulder fully and throw a ball well. Since it has been reported that PES has a better prognosis and responsiveness to chemotherapy than intramedullary Ewing's sarcoma, we believe that such reduction surgery with photodynamic therapy might be the strategy of choice to obtain satisfactory limb function in cases of PES.

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