UNASSIGNED: The authors present five cases of @entity1048 located in the femur (4) and tibia (1) in @entity1 and young adults (1 female and 4 males) with an age range of 9 - 23 years (mean age 15 years). Radiographs in all cases showed a broad-based soft tissue mass attached to the cortex with periosteal reaction and in two of them cortical disruption with extensive medullary involvement. Follow-ups were available in four cases (range 11 - 73 months) and revealed pelvic @entity3 after 15 months with ultimately rapid dissemination and death in a 9-year-old @entity1 and @entity3 to the humerus after 13 months in a 15-year-old @entity1 . The former @entity5 widely extended into the medullary cavity and an amputation was carried out, the latter had a pure juxtacortical position and an en block resection was performed; both of them were treated with chemotherapy. All the lesions displayed distinctive structural patterns combining a large island of tumorous cartilage and hypocellular, bland-looking myxoid mesenchymal stroma with abrupt transition between both components. @entity421 , the delicate @entity10545 were produced by innocuous stromal cells lacking apparent atypia. They were strictly situated outside the prevailing chondroid areas and disclosed sometimes only after a meticulous search. Immunohistochemical detection of @entity52988 , @entity2281 protein and D2-40 assisted effectively not only in recognition of the real stromal histogenetic derivation, but also in distinction of true differentiation of a heavily mineralized extracellular matrix. Molecular analysis revealed no @entity8725 mutation in four examined cases. Regardless of unique low-grade morphology in rare @entity1048 , an aggressive therapeutical approach similar to @entity421 is justified, particularly in the case of a medullary extension.

[ XXXX - personal experience with five cases].

@entity1 :: ('9606', 'Species') :: ['children', 'girl', 'boy'] @entity5 :: ('MESH:D009369', 'Disease') :: ['tumor'] @entity10545 :: ('MESH:D010017', 'Disease') :: ['flocculent osteoid deposits'] @entity52988 :: ('23314', 'Gene') :: ['SATB2'] @entity421 :: ('MESH:D012516', 'Disease') :: ['conventional osteosarcoma', 'Contrary to conventional osteosarcoma'] @entity8725 :: ('3417;3418', 'Gene') :: ['IDH1/2'] @entity3 :: ('MESH:D009362', 'Disease') :: ['metastasis'] @entity2281 :: ('6271', 'Gene') :: ['S100'] @entity1048 :: ('MESH:D010522', 'Disease') :: ['periosteal osteosarcoma']
@entity1048 :: (MESH:D010522,Disease) :: ['Periosteal osteosarcoma']
