Molecular Characterization and Its Clinical Application of GNAS Variants in Intramuscular Myxoma

Intramuscular myxoma (IM) is a benign tumor that harbors GNAS missense variants. Distinguishing IM from low-grade myxofibrosarcoma (LGMFS) is challenging due to similarities in imaging and histological features. While molecular analysis aids differentiation, the low number of tumor cells available for DNA extraction necessitates highly accurate detection methods for variant identification. The aim of this study was to delineate molecular characteristics using next-generation sequencing (NGS) and to propose an optimal screening method in a clinical setting to differentiate IM from LGMFS.

Ten IM cases and nine LGMFS cases with extractable DNA from FFPE samples were recruited.

A custom NGS panel-based analysis for GNAS revealed R201C/R201H variants in resected samples of eight cases with IM and in none of the eight cases, excluding one with insufficient sample quality, with LGMFS, and in biopsy samples of both available cases with IM. Additionally, various sequence alterations were detected irrespective of the clinical status (IM, LGMFS, and normal tissue) or sample conditions (resected, biopsy, and relapsed). The detection rate of GNAS-positive IM using other methods (PCR-direct sequencing, fragment signal analysis using restriction digestion and capillary electrophoresis after PCR combined with peptide nucleic acid (PNA) clamping, and PCR-direct sequencing combined with PNA clamping) was calculated as 0.42, 0.83, and 0.75, respectively, while the detection rate for GNAS-negative LGMFS was 1.

These findings suggest that fragment signal analysis is a reasonable diagnostic approach for differentiating IM from LGMFS. However, it is important to recognize that the absence of GNAS R201C/R201H variants does not rule out IM.