<prompt> A 5-year old boy presents with pain and swelling in diaphysis of tibia. He also complains of fever. On examination, his ESR was raised. Which of the following is the likely diagnosis?Ewing sarcomaChondrosarcomaOsteogenic sarcomaFibrosarcoma  <response>: Ans. a. Ewing sarcoma Ref: Apley 9e pe p 212-13; Tureks 6e pe p 307; Campbells 11e pe p 910-913; Harrisons 19e 119e-4, 18e pe p820A 5-year old boy presents with pain and swelling in diaphysis of tibia. He also complains of fever. On examination, his ESR was raised. Ewing sarcoma is the most likely diagnosis.Ewings SarcomaArises from endothelial cells of the bone marrow in the diaphysis medullary cavity of long tubular bonesQ especially femur and flat bones of pelvis.Highly malignant, undifferentiated peripheral primitive neuroectodermal tumor PNETMC site: Diaphysis of femurQ fibula ilium tibia.Pathology:Arising in medullar cavity usually invade the cortex, and periosteum producing a soft tissue massQ.Composed of sheets of uniform, small round cellsQ that are slightly larger than lymphocytes, with pale clear appearing cytoplasm due to presence of glycogenQ.Cytoplasm is PAS positive and diastase digestibleQ.Presence of Homer-wright rosettes and pseudo rosette is indicative of neural differentiation i.e. PNETExpress MIC 2 gene in very high amount, distinguish from other round cell tumorsQ.Most definitive test: Demonstration of chromosomal translocation by karyotyping or RT- PCR detection of t11 : 22.80- 95 patients have a translocation mostly t 11: 22 t 21 : 22 and rarely t 7 : 22QEwing sarcomas are periodic acid Schiff positive owing to intracellular glycogen and reticulin negative.Clinical Feature:Mostly in males between 10-20 years of ageQ.Pain, swelling, tenderness, urinaryrectal complaints when ilium involved pathological fracture.Systemic symptoms such as fever, generalized weakness, weight loss, and lab anomalies as anemia, leukocytosis and raised ESRQ are hallmark of fulminating course, advanced disease or metastasis.50 of all metastases occurs to lungQ and 25 to bone and bone marrowDiagnosis:Mottled rarefaction of spongiosa with permeation of overlying cortex, reflecting rapid bone destruction is the principal findingLaminated layered periosteal new bone formation known as onion-peel appearanceSoft tissue massQ, indicating neoplasm has perforated cortexTreatment:Highly radiosensitive melts on radiotherapyQ but overall survival is not much enhancedChemotherapy is much more effective and include vincristine, actinomycin D, adriamycin, ifosfamide and etoposideBest results are achieved by:Preoperative chemotherapy then wide excision or amputation if tumor is in favorable site and further chemotherapy for 1 years.Radiotherapy followed by local excision if it is in less accessible site and then further chemotherapy for 1 yearPoor prognostic factors for Ewings sarcoma Distant metastases Advanced and extensive disease with fulminant course. Large tumor size 8cm Proximal location Older age 17 years Mate gender Genetic aberrant P-53 expression Relapse Early within 1 year relapseHistological grade have no prognostic significance because all Ewings sarcoma are considered as high grade.Histological response to neoadjuvant chemotherapy is a good prognostic indicator. 