BCOR-Altered Sarcoma in a 6-Month-Old: Diagnostic Challenges and Morphological Insights

Area of Science:

• Oncology
• Pathology
• Genetics

Background:

• BCOR-altered sarcomas (BAS) are a challenging diagnostic group of undifferentiated small round cell sarcomas.
• Morphological overlap with other pediatric neoplasms complicates BAS diagnosis.

Purpose of the Study:

• To report a rare case of BCOR-altered sarcoma (BAS) in an infant with unusual rhabdoid features.
• To highlight the diagnostic utility of integrated histopathological, immunophenotypic, and molecular analyses in BAS.

Main Methods:

• Case report of an infant with retroperitoneal mass and bilateral lower limb weakness.
• Histopathological examination revealing small round cells, spindle cells, and prominent rhabdoid cells.
• Immunohistochemistry (BCOR, Cyclin D1, TLE-1, BCL-6, SATB2, INI1, BRG) and fluorescence in situ hybridization (FISH) for molecular profiling.

Main Results:

• The tumor exhibited a mixed morphology with significant rhabdoid components.
• Immunohistochemistry confirmed BCOR positivity and retained INI1/BRG expression.
• FISH excluded BCOR::CCNB3 fusion and NTRK rearrangements, supporting the BAS diagnosis.
• The patient responded favorably to Ewing sarcoma chemotherapy.

Conclusions:

• BCOR-altered sarcomas can present with prominent rhabdoid morphology, expanding the known histopathological spectrum.
• A comprehensive diagnostic approach combining histology, immunohistochemistry, and molecular testing is crucial for accurate BAS diagnosis.
• Early diagnosis and appropriate chemotherapy, such as the Ewing sarcoma regimen, can lead to favorable outcomes in BAS.