Ewing's sarcoma

Ewing's sarcoma is an aggressive malignant neoplasm composed of small round blue cells that predominantly arises within the bones—commonly the pelvis, femur, and other long bones—or less frequently in adjacent soft tissues.

It most frequently affects children, adolescents, and young adults, typically manifesting with localized bone pain, swelling, and palpable soft-tissue masses.

Pathophysiologically, the disease is defined by characteristic chromosomal translocations fusing the *EWSR1* gene with an ETS family transcription factor, most commonly generating the *EWSR1::FLI1* fusion oncoprotein that drives aberrant transcription and oncogenesis.

Ewing's sarcoma is clinically notable for its high propensity for early micrometastatic and overt hematogenous spread, most frequently involving the lungs, distant bones, and bone marrow.