<prompt> 12 year old boy presents with progressive swellings at upper end of tibia - irregular, local temperature raised, invariable consistency and ill defined margins most probable diagnosis isGiant cell tumorEwings sarcomaOsteogenic sarcomaSecondary metastasis  <response>: The clinical presentation in question can occur both in Ewings sarcoma and osteosarcoma. However, swelling is around the knee joint at upper end of tibia, which ours the diagnosis of osteosarcoma metaphyseal lesion. Ewings sarcoma usually occurs in the diaphysis of the bone middle of the shaft. Giant cell Tumor site- Epiphysis Secondary metastasis occurs in old age usually. 