Review Question - QID 4582

Based on the presentation and clinical findings, the most likely diagnosis is Ewing’s sarcoma. The associated translocation and fusion protein is t (11:22), EWS-FL1.

Ewing’s sarcoma, the second most common primary tumor of bone in children, is the result of a translocation event; the resulting protein, EWS-FL1, is seen in all cases. PCR can be used to detect the gene, which can help to discern this from other round cell tumors. Elevated LDH levels and concomitant p53 mutations are noted to be poor prognostic factors.

Burchill et al. reviews the histologic, diagnostic and prognostic considerations of Ewing’s sarcoma. Under light microscopy the tumor is found to be composed of small round cells containing finely dispersed chromatin. They emphasize the importance of research into the fusion proteins as targets for therapeutic intervention.

Figure A shows a swollen limb in a patient with Ewing’s sarcoma of the thigh. Figure B is an AP radiograph of a femur, where significant periosteal reaction is giving the femoral diaphysis an “onion skin” appearance. Figure C demonstrates the small blue cells that comprise Ewing’s sarcoma on a histological level. Ewing’s will also have CD99 immunostaining reactivity.

Incorrect Answers
1: t (x:18) is the translocation associated with synoval sarcoma. The fusion protein is SYT-SSX1
2: t (2: 13), PAK3-FKHR is the translocation and associated protein for rhabdomyosarcoma
4, 5: t (9:22) and EWS-CHN are the translocation and associated fusion protein for chondromyxoid sarcoma