Synonyms

Juxtacortical osteosarcoma

Definitions

Bone
ICD-O-3 topography code:	C40-C41
ICD10:	C40-C41

Parosteal osteosarcoma is a low grade osteosarcoma arising from the surface of bone. Approximately 70% of cases affect the distal posterior femur; other common sites are the proximal tibia and the proximal humerus. The tumour presents as a heavily mineralized, lobulated mass attached to the underlying cortex and shows a tendency to wrap around the involved bone. Histologically, parosteal osteosarcoma consists of parallel bony trabeculae in a hypocellular stroma. About 50% of the tumours show cartilaginous differentiation ¹

Fletcher CDM, Unni KK, Mertens F (Eds.)
World Health Organization Classification of Tumours. Pathology and Genetics of Tumours of Soft Tissue and Bone.
3rd Edition
IARC Press: Lyon 2002

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Parosteal osteosarcoma predominantly affects young adults, with a slight predilection for females. The prognosis after complete excision is usually excellent; marrow invasion and moderate cytological atypia do not predict a worse outcome. If incompletly excised, the tumour may reccur and dedifferentiate; such dedifferentiation is associated with a prognosis similar to that of conventional osteosarcoma ²

Fletcher CDM, Unni KK, Mertens F (Eds.)
World Health Organization Classification of Tumours. Pathology and Genetics of Tumours of Soft Tissue and Bone.
3rd Edition
IARC Press: Lyon 2002

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