Abstract
Osteosarcoma (OS) is the most common primary non hematopoietic malignant tumor of bone with a strict histologic definition: the presence of unequivocal osteoid produced by neoplastic cells. Rare variants displaying low-grade histological features have been described; among which chondromyxoid fibroma-like (CMF-OS) is the rarest. However, despite its bland morphology; CMF-like OS has an aggressive clinical behavior and a poor prognosis. To the best of our knowledge, only 3 cases of CMF-OS have been previously reported in children. Because of its atypicality and scarcity; misdiagnosis is more likely to occur. Herein we describe a new case of CMF-OS in a 13 years old girl with fatal outcome. Diagnosis was based on focal malignant bone formation and correlation with imaging studies. The aim of the present case presentation is to raise awareness of this rare entity and to highlight the challenging diagnosis.