The diagnosis of @entity3478 , which only account for 1% of @entity5 in @entity1 , represents quite a challenge for the pathologist. Apart from the often overlapping morphology between different entities, heterogeneity within one and the same @entity5 has to be kept in mind. Furthermore, in most cases the diagnosis must be established based on small biopsy specimens and occasionally even on frozen sections. In this context detailed clinical information including the @entity1 's age and exact localization of the @entity5 , as depicted by X-ray or MRI, are essential requirements for a correct diagnosis. In addition, multiple biopsies from different @entity5 sites may be of help. For example, 25% of @entity421 ( @entity421 ) are chondroplastic. Others may contain areas similar to @entity1492 ( @entity1492 ) or @entity1418 ( @entity1418 ). Since 90% of @entity421 occur in the second decade of life whereas @entity511 , @entity1492 and @entity1418 usually manifest after the age of 40 years, a biopsy solely composed of malignant chondromatous tissue obtained from a tibial lesion of a 10-year-old @entity1 should most likely be considered as part of an @entity421 . In the differential diagnosis of the so-called small, round cell @entity5 , which include @entity2828 , @entity706 and small-cell @entity421 , immunohistochemical staining of the paraffin-embedded material and a molecular biological/genetic work-up of frozen material are most helpful. In this paper the histomorphological characteristics and criteria for differential diagnosis of the most common @entity3478 are discussed.

[Special diagnostic problems in XXXX ].

@entity1 :: ('9606', 'Species') :: ['humans', 'patient', 'child'] @entity2828 :: ('MESH:D012512', 'Disease') :: ['Ewing sarcoma'] @entity511 :: ('MESH:D002813', 'Disease') :: ['chondrosarcomas'] @entity706 :: ('MESH:D008223', 'Disease') :: ['malignant lymphoma'] @entity3478 :: ('MESH:D001859', 'Disease') :: ['primary malignant bone tumors'] @entity5 :: ('MESH:D009369', 'Disease') :: ['tumor', 'tumors', 'malignancies'] @entity1418 :: ('MESH:D051677', 'Disease') :: ['MFH', 'malignant fibrous histiocytoma'] @entity1492 :: ('MESH:D005354', 'Disease') :: ['FSA', 'fibrosarcoma'] @entity421 :: ('MESH:D012516', 'Disease') :: ['OSA', 'osteogenic sarcomas']
@entity3478 :: (MESH:D001859,Disease) :: ['primary malignant bone tumors']
