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## ABSTRACT

Rhabdomyosarcoma (RMS) is a highly aggressive pediatric cancer known for its therapeutic challenges, particularly when it becomes metastatic or recurrent. Traditional treatment approaches have shown limited success, prompting a growing interest in targeted therapies. The emergence of next-generation sequencing (NGS) has revolutionized our ability to identify actionable mutations in RMS, offering the promise of personalized treatments and improved patient outcomes. A recent case involving a 3-year-old child diagnosed with embryonal RMS highlighted the potential of next-generation sequencing (NGS) in clinical practice. Despite receiving initial chemotherapy, the patient’s tumor showed progressive growth. What made this case particularly intriguing was the discovery of co-occurring somatic mutations in the RAS/MAPK pathway, specifically in BRAF and HRAS genes, which are traditionally believed to be mutually exclusive.
Notably, the BRAF mutation identified in this case, N581I, is a non-classical (Class III) hotspot mutation that had not been previously reported in embryonal RMS. This novel finding underscores the critical importance of comprehensive genetic profiling in pediatric cancers and suggests the existence of potential therapeutic avenues that target BRAF alterations.
In conclusion, the integration of NGS technologies in clinical practice holds great promise for identifying previously unrecognized mutations in pediatric cancers like RMS. These findings have the potential to open up new treatment options and improve outcomes for young patients facing this aggressive disease.

## INTRODUCTION

Rhabdomyosarcoma (RMS) is an aggressive pediatric cancer originating from embryonic mesenchymal tissue1, and remains a formidable therapeutic challenge due to its ability to manifest in diverse anatomical sites2. Despite conventional treatments, including chemotherapy, surgery, and radiotherapy, the overall survival rate for metastatic and recurrent RMS patients remains low. This bleak scenario has propelled interest in exploring targeted therapies, particularly in high-risk patients and those with aggressive and relapsed disease. Recent advancements in next-generation sequencing (NGS) and computational analyses have revolutionized the study of somatic mutations across various cancer types, shedding light on novel opportunities for precision medicine in RMS and beyond.
Sidra Medicine, the single pediatric cancer care institution in Qatar, has initiated the Sidra Pediatric Precision Oncology Program, aiming to provide research-grade tumor sequencing for pediatric solid tumor patients. This initiative offers an unparalleled avenue for molecular characterization that guides both diagnosis and treatment.
In this context, we present a case report of a young patient with embryonal RMS, treated at Sidra Medicine. In our patient, we identified the co-occurrence of two actionable mutations in the HRAS and BRAF genes part of the RAS/MAPK pathway. These mutations are traditionally observed as mutually exclusive, and their combination has never been reported (to our knowledge) in embryonal RMS.

## METHODS

Informed written consent was obtained from the patient for participation in the study (SDR SDR200074 / IRB 1509000). The institutional review board approved this study (conducted at Sidra Medicine). At presentation, his tumor was diagnosed with the standard histopathological examination at the referring center. At the time of progression, further analysis was carried out on the tumor DNA extracted from the FFPE specimen by next-generation sequencing (NGS) technique.