Epithelioid sarcoma of the scalp: a case report and literature review.

: Epithelioid sarcoma (ES) is an aggressive mesenchymal tumor exhibiting bi-directional phenotypes. According to its proclivity for different sites, ES can be subdivided into two categories: distal and proximal variants. Proximal ES often affects the truncal tissue, thighs, head, and neck. Accumulating evidence indicates that several locations in the head, including the orbital, gingival, and nasal cavities, are involved in ES. However, the underlying mechanisms of ES carcinogenesis and progression are largely unknown, including and especially the reason why the tumor cells are positive for both epithelial and mesenchymal classical markers. Thus, we wish to share a rare case of ES in the scalp and its clinical and molecular features. Only 9 cases to date have been reported. An 80-years-old man had sustained a painful swollen mass in his scalp for three months. A diagnosis of epithelioid sarcoma was established based on the combination of the histopathological and immunohistochemical findings. The tumor cells were positive for both mesenchymal (vimentin and S100) and epithelial markers (pan-cytokeratin). This case suggests that ES can be derived from the soft tissue of the scalp. The tumor cells co-expressed biomarkers of epithelial and mesenchymal cells, suggesting the mesenchymal-epithelial transition (MET) may be involved.