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Case Reports

Abstract

Cellular myofibroma (MF) is a benign mesenchymal tumor frequently encountered in the subcutaneous tissue, notably in the head-neck area. Its rarity often complicates diagnosis, especially in distinguishing it from myogenic differentiated sarcoma. The exact cause of this tumor remains elusive. While most cases occur sporadically, there are indications of potential familial inheritance, possibly through autosomal dominant or recessive traits. Mutations in PDGFRB have been linked to MF, and there have been observed associations between cellular myofibroma and SRF-RELA gene fusions. Herein, we present a case of a 10-year-old girl presented with a raised, firm skin mass on the left temporal region that had noticeably grown over the past month. Ultrasound examination revealed a subcutaneous soft tissue mass above the underlying temporalis muscle, without extending deeply. Following surgical excision, histologic sections revealed a cellular, infiltrative spindle cell proliferation with myofibroblastic morphology, demonstrating a multinodular architecture interspersed with areas of eosinophilic hyalinization. Focal areas exhibited an increased mitotic activity, reaching up to 6 mitoses per 10 high-power fields (HPF), although necrosis was not identified. The neoplastic cells showed positive staining for SMA, focal positivity for desmin, and negative staining for SOX10, ALK, TRK, CD34, S100, STAT6, and beta-catenin. Notably, the lesion displayed an infiltrative pattern and involved both peripheral and deep surgical margins. No gene fusion was detected on the sarcoma-targeted gene fusion panel. The tumor showed striking similarities to cellular myofibromas with recurrent SRF gene fusions. Given the propensity of local recurrence, a complete surgical excision was recommended.