New Bone Sarcoma

To present a rare case of bone sarcoma with a novel translocation. H&E sections, extensive immunohistochemical stains and subsequently FISH studies were performed. The tumor was approached as a small blue cell sarcoma. immunohistochemical stains showed tumor to be negative for myogenin, desmin, S100, synaptophysin, NF, FLI-1,EMA and pancytokeratin. CD56 and BCL2 were positive.CD99 was positive. However, FISH was negative for EWSR1 gene rearrangement. SYT(SS18) FISH for synovial sarcoma was negative too. No osteoid was present in the biopsy. The working diagnosis was undifferentiated sarcoma. FISH abroad was done for the fusion CIC-DUX4 t(4;19) that occurs in some cases of undifferentiated sarcoma and it was negative. Finally, this sarcoma was positive for BCOR-CCNB3 gene fusion by FISH, a novel translocation recently described. The diagnosis of small round cell sarcoma in the pediatric population is not always straight forward. This case shows the increasing importance of molecular testing for the diagnosis of the more difficult cases, beside the influence of the molecular changes both on the treatment and the prognosis.