Primary Dedifferentiated Parosteal Osteosarcoma in a 21-Year-Old Man

Abstract not available. Introduction provided instead.

Surface osteosarcomas are a group of tumors that account for approximately 4% to 10% of reported osteosarcomas.^1,2 There are 4 types of surface osteosarcomas: parosteal, periosteal, dedifferentiated parosteal, and high-grade surface.^2,3 Conventional parosteal osteosarcoma (c-POS) is the most commonly occurring variant; it accounts for approximately 75% of diagnosed surface osteosarcomas.^2,4 It is characterized as a low-grade (Broders grade 1-2), slow-growing malignant tumor arising from the juxtacortical tissues with low potential for metastasis and a good prognosis after surgical resection.^3,5-7

Dedifferentiated POS (dd-POS) is a variant in which a low-grade c-POS is associated with a high-grade sarcoma either at time of presentation (primary dd-POS) or time of recurrence (secondary dd-POS). Such tumors are associated with a higher rate of systemic metastasis and a worse prognosis when compared with c-POS cases.^3,5,6,8,9

We describe the case of a patient who presented with a distal femur lesion that was thought to be a low-grade c-POS, but was subsequently found to be primary dd-POS. This case illustrates the difficulties in correctly diagnosing such tumors.