[Parosteal osteosarcomas: unusual findings].

Objective: To study and evaluate the unusual findings in the natural history of parosteal osteosarcomas. Parosteal osteosarcomas are well-differentiated tumours of low grade malignancy, but may dedifferentiate into a more aggressive lesion.
Material and Methods: We reviewed 7 parosteal osteosarcomas treated in La Paz Hospital between 2005 and 2009 (3 were dedifferentiated parosteal osteosarcomas). The authors analysed the clinical and radiological features, histology, treatment and outcomes in this patient group.
Results: There were 5 men and 2 women, with a mean age of 32.14 years, range 24-47 years. Three of seven tumours (42.8%) were dedifferentiated osteosarcomas. All three patients received chemotherapy. One patient presented with pulmonary metastases. No patient died.
Conclusions: It is important to understand that the biological phenomenon of dedifferentiation can occur in parosteal osteosarcomas. The prognosis, treatment and survival changes radically.
(Copyright © 2011 SECOT. Published by Elsevier España, S.L. All rights reserved.)