EWSR1::BEND2 fusion sarcoma in bone: a report of two rare cases.

The two cases, we had presented here, were extremely rare instances of the EWSR1::BEND2 fusion sarcomas in bone. The first case was a 12-year-old female with a 50 × 25-mm lytic tumor in metatarsal bone. Histopathologic examination revealed a widespread cellular, fascicular forming, spindled cell component along with a focal round cell component. CD99 was diffuse membranous positive while cytokeratin and EMA were focal positive. The second case was a 62-year-old female with a pathological fracture in femur. On MRI examination, a heterogeneous tumor measuring 96 × 54 mm was detected in the femur, extending into the soft tissue. Histopathologic examination revealed a high-grade lesion consisting of round cells. CD56, CD99, and cytokeratin were focal positive. EWSR1::BEND2 fusion has previously been reported in a subtype of astroblastoma and other rare entities that we discuss in this work.