Abstract：
Myoepithelial carcinoma (MC) arises from the myoepithelial cells. It is a rare tumor with a predilection for salivary glands. MC in soft tissue is uncommon. Soft tissue MC exhibits dual epithelial and smooth muscle phenotype. The extremities and limb girdles are commonly affected. We present cytological findings of retroperitoneal MC with an accurate diagnosis being rendered with the aid of immunocytochemistry on the cell block and demonstration of EWSR1 rearrangements by fluorescence in situ hybridization on cytology smear. The smears were cellular, showing loose clusters and sheets of tumor cells embedded in dense eosinophilic to myxoid matrix material. The cells were oval to polygonal, with focal areas showing moderate nuclear pleomorphism, vesicular to coarse chromatin, and vacuolated cytoplasm with clearing. On immunocytochemistry, tumor cells were positive for epithelial membrane antigen, pan-cytokeratin, calponin, smooth muscle actin, and S-100. A literature review shows only a handful of cases of soft tissue MC. The current report emphasizes the need for cytomorphological awareness with the employment of ancillary testing for accurately diagnosing this rare tumor at an uncommon location. We also discuss the diagnostic challenges and troubleshooting.
摘要：
肌上皮癌（MC）起源于肌上皮细胞。这是一种罕见的肿瘤，好发唾液腺。软组织中的MC并不常见。软组织MC表现出双重上皮和平滑肌表型。四肢和四肢腰带通常受到影响。我们提供了腹膜后MC的细胞学发现，并借助细胞块上的免疫细胞化学进行了准确的诊断，并通过细胞学涂片上的荧光原位杂交证明了EWSR1重排。涂片是细胞的，显示出松散的肿瘤细胞簇和薄片，它们嵌入在致密的嗜酸性粒细胞到粘液样基质材料中。细胞呈椭圆形到多边形，焦点区域显示中等核多态性，囊泡至粗染色质，和空泡状的细胞质。关于免疫细胞化学，肿瘤细胞上皮膜抗原阳性，泛细胞角蛋白，Calponin,平滑肌肌动蛋白，S-100文献综述显示只有少数软组织MC病例。当前的报告强调需要对细胞形态学的认识，并采用辅助测试来准确诊断这种罕见的肿瘤。我们还将讨论诊断挑战和故障排除。
