A case of a paediatric chondromyxoid fibroma-like osteosarcoma.

Chondromyxoid fibroma-like osteosarcoma (CMF-OS) is an exceptionally rare and low-grade variant of osteosarcoma, as classified by the World Health Organization. Misdiagnosis is common in CMF-OS, often leading to delays in definitive surgical intervention. CMF-OS exhibits variable imaging features, frequently mimicking chondromyxoid fibroma. It may present as osteolytic, osteogenic, or expansive lesions, often associated with soft tissue invasion, cortical disruption, and occasionally a periosteal reaction. Cases have been reported in diverse anatomical locations, including the craniofacial region and bones of the lower limbs. Histologically, CMF-OS is distinguished by its unique mucoid appearance, characterized by loose aggregates of stellate and spindle-shaped tumour cells embedded within a highly myxoid stroma. Surgical resection remains the cornerstone of treatment for CMF-OS, emphasizing the importance of accurate diagnosis to facilitate timely and appropriate management.