Hsiao C H, Cheng C J, Yeh K L
Department of Pathology, National Taiwan University Hospital, Taipei, ROC.
J Formos Med Assoc. 1997 Mar;96(3):209-12.
Myoepithelioma is a rare salivary gland tumor which is composed exclusively of myoepithelial cells. Histologically, it can be divided into three cell types: spindle, plasmacytoid and mixed type. Malignant myoepithelioma is characterized by invasive growth. In March 1995, a 60-year-old man presented with a left cheek tumor which he had first noted 2 years previously. Computed tomography revealed a large expansile tumor in the maxillary sinus with invasion into the surrounding soft tissue. Partial resection of the tumor was performed because of extensive involvement of the surrounding tissue. The patient died due to spread to the brain 5 months after surgery. Histologically, the tumor was composed exclusively of plasmacytoid cells, with bone destruction. Immunohistochemically, these cells were negative for immunoglobulin light chains (kappa and lambda) and heavy chains (Ig G, A, M) but positive for S-100, cytokeratin, actin and vimentin.Ultrastructurally, the tumor cells contained numerous randomly oriented actin-like microfilaments in the cytoplasm, and had desmosomes on the cell membrane. Malignant plasmacytoid myoepithelioma of the maxillary sinus was diagnosed. In addition to our case, only five cases of pure plasmacytoid myoepithelioma have been reported. Plasmacytoid myoepithelioma tends to occur in the minor salivary glands and has more aggressive behavior than spindle cell myoepithelioma. Morphologically, it is very difficult to differentiate plasmacytoid myoepithelioma from plasmacytoma and immunohistochemical staining is necessary to make a correct diagnosis.
肌上皮瘤是一种罕见的唾液腺肿瘤，仅由肌上皮细胞组成。从组织学上看，它可分为三种细胞类型：梭形、浆细胞样和混合型。恶性肌上皮瘤的特征是浸润性生长。1995年3月，一名60岁男性因左脸颊肿物就诊，该肿物他2年前就已发现。计算机断层扫描显示上颌窦有一个巨大的膨胀性肿瘤，并侵犯周围软组织。由于周围组织广泛受累，对肿瘤进行了部分切除。患者术后5个月因肿瘤扩散至脑部死亡。组织学上，肿瘤仅由浆细胞样细胞组成，并伴有骨质破坏。免疫组化显示，这些细胞免疫球蛋白轻链（κ和λ）和重链（Ig G、A、M）呈阴性，但S-100、细胞角蛋白、肌动蛋白和波形蛋白呈阳性。超微结构上，肿瘤细胞胞质内含有大量随机排列的肌动蛋白样微丝，细胞膜上有桥粒。诊断为上颌窦恶性浆细胞样肌上皮瘤。除我们的病例外，仅报道过5例纯浆细胞样肌上皮瘤。浆细胞样肌上皮瘤倾向于发生在小唾液腺，且比梭形细胞肌上皮瘤具有更强的侵袭性。在形态学上，浆细胞样肌上皮瘤与浆细胞瘤很难鉴别，需要进行免疫组化染色才能做出正确诊断。
