Synchronous Low-Grade Central Osteosarcoma and Ewing Sarcoma: A Rare Case Report.

Area of Science:

• Oncology
• Orthopedic Oncology
• Rare Tumors

Background:

• Cauda equina syndrome presentation in a young female.
• Initial diagnosis of a lumbar spine lesion.
• Identification of a secondary distal femur mass.

Purpose of the Study:

• To report a unique case of synchronous bone malignancies.
• To characterize the diagnostic pathway for rare tumors.
• To discuss the extreme rarity of co-occurring Ewing sarcoma and low-grade central osteosarcoma.

Main Methods:

• Magnetic Resonance Imaging (MRI) for lesion detection.
• Core needle biopsy and surgical resection for histopathological analysis.
• Immunohistochemistry (CD99, FLI1, SATB2) and Next-Generation Sequencing (EWSR1::FLI1 fusion) for molecular characterization.
• Fluorescence In-Situ Hybridization (FISH) for MDM2 gene amplification.

Main Results:

• Lumbar lesion diagnosed as Ewing sarcoma based on morphology, immunophenotype (CD99+, FLI1+), and EWSR1::FLI1 fusion.
• Distal femur lesion diagnosed as low-grade central osteosarcoma (LGCOS) based on histomorphology and SATB2 positivity.
• Synchronous presentation of both genetically distinct tumors within six months.
• Calculated extremely low probability (1 in 7.5 trillion) of this dual occurrence.

Conclusions:

• This case represents an exceptionally rare instance of synchronous Ewing sarcoma and LGCOS.
• The diagnostic workup highlights the importance of comprehensive histopathological and molecular analysis.
• The extreme rarity underscores the unique biological and statistical nature of this patient's presentation.