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Case Reports

Abstract

Recent literature suggests that there is a rare emerging group of cellular pericytic myoid neoplasms defined by bland spindle cell proliferation, brisk mitosis, incomplete muscle expression, lack of desmin reactivity, SRF::ICA1L gene fusion, and potential for malignant behavior.  Angiomyomas, also known as vascular leiomyomas, represent the fully mature smooth muscle phenotypic end of the spectrum of pericytic myoid tumors and have not been previously known to harbor this gene fusion. We report a case of a 24-year-old male with a history of a right great toe mass, initially noticed three to four months prior, which progressively enlarged and became painful. The mass was completely excised to reveal a well-circumscribed bland spindle cell neoplasm with eosinophilic cytoplasm, arranged in a fascicular pattern around dilated, thick-walled vascular channels. There were no discernible mitotic figures or necrosis. The lesional cells were strongly and diffusely positive for SMA, SMMS, Desmin, and H-Caldesmon (focal), SATB2, AE1/3 (focal), and negative for EMA, HMB45, Beta-Catenin, MUC4, ERG, CD34, S100, SOX10, ER, and PR. The Ki-67 proliferative index was estimated at <1%.  RNA-Seq gene fusion analysis identified SRF::ICA1L fusion transcript, a novel finding in angiomyoma, but previously described in cellular myoid neoplasms. No other pathogenic mutations were detected by the solid tumor DNA NGS panel. Intriguingly, our case lacked the typical brisk mitotic activity and loss of desmin expression that was initially thought to define an emerging group of pericytic myoid tumors, suggesting that SRF::ICA1L gene fusion may not necessarily be unique or definitional as previously thought.