Bone and soft-tissue sarcomas — branching viva

Outpatient clinic: a thirteen-year-old boy with three months of deep night pain in the distal thigh and a firm mass just above the knee, and a plain radiograph showing a mixed lytic and sclerotic distal femoral metaphyseal lesion with sunburst spicules and a Codman triangle. The examiner asks: name the diagnosis, give the staging panel and the biopsy principle, then branches to the chemotherapy backbone and the histologic response, to the same lesion re-presenting as a diaphyseal permeative lesion with systemic symptoms that reframes it as Ewing sarcoma and its EWSR1-FLI1 fusion, and finally to a head-and-neck mass that opens the rhabdomyosarcoma and its PAX-FOXO1-driven risk groups.