Fusion-Negative Rhabdomyosarcoma: Clinical Application of Targeted RNA Sequencing.

Area of Science:

• Pediatric Oncology
• Molecular Pathology
• Cancer Genomics

Background:

• Rhabdomyosarcoma (RMS) is the most frequent soft tissue sarcoma in childhood.
• Subtyping of RMS into fusion-positive and fusion-negative (FN-RMS) is crucial for treatment stratification.
• FN-RMS encompasses embryonal and spindle cell/sclerosing subtypes, characterized by the absence of the PAX::FOXO1 fusion.

Purpose of the Study:

• To investigate the pathologic and molecular landscape of fusion-negative rhabdomyosarcoma (FN-RMS).
• To utilize a targeted next-generation sequencing RNA-Seq (NGS RNA-Seq) assay for comprehensive molecular profiling.
• To correlate molecular findings with clinicopathological features in a cohort of pediatric FN-RMS.

Main Methods:

• Analysis of 12 FN-RMS tumors using targeted RNA-Seq with the Illumina Trusight Pancancer panel.
• Correlation of identified molecular alterations with patient clinicopathological data.

Main Results:

• Identified mutations in signaling molecules (KRAS, HRAS, NRAS, FGFR4) in embryonal rhabdomyosarcomas (ERMS).
• Detected oncogenic DICER1 mutations in 2 ERMS, and TP53/NF1 mutations in an anaplastic ERMS.
• Discovered gene fusions TEAD1::NCOA2 and FUS::TFCP2 in spindle cell/sclerosing rhabdomyosarcoma (SSRMS) subtypes.

Conclusions:

• A combined morphological and molecular diagnostic approach using targeted RNA-Seq is effective for pediatric FN-RMS.
• This methodology aids in identifying clinically actionable molecular alterations.
• The study highlights the molecular heterogeneity within FN-RMS, informing potential therapeutic strategies.