化生性胸腺瘤临床病理分析

Clinicopathologic study of metaplastic thymoma

目的探讨化生性胸腺瘤的临床病理特点。方法应用光镜、免疫组织化学（EnVision法）染色[单克隆抗体选用AE1／AE3、波形蛋白、上皮膜抗原（EMA）、CD3、CD5、CD20、CD34、CD57、CD99、末端脱氧核苷酸转移酶（TdT）、HMBE·1、calretinin、053和Ki-67]和透射电镜观察3例化生性胸腺瘤的组织学特点、免疫学表型和超微结构。结果3例化生性胸腺瘤均为女性，年龄为33、58和45岁。组织学表现为双相分化特征，上皮细胞区域与梭形细胞区域交错分布并相互移行。上皮细胞区域的细胞轻度异型，有核沟和核内假包涵体，核分裂象罕见，呈岛状和条索状排列并相互吻合；梭形区域细胞形态温和，未见核分裂象，排列成束状或席纹状结构。免疫组织化学染色：上皮细胞区域AE1／AE3强阳性表达，不表达波形蛋白和CD5，Ki-67指数3％-5％；梭形细胞区域波形蛋白弥漫表达，EMA阳性，不表达CD5和CD20；间质淋巴细胞CD3阳性，不表达TdT和CD99。超微结构示上皮细胞区域细胞间有桥粒和半桥粒结构，而梭形细胞区域缺乏。结论化生性胸腺瘤是一类罕见的具有独特临床病理特征的良性或低度恶性胸腺上皮来源肿瘤。

Objective To study the clinicopathologic characteristics of metaplastic thymoma. Methods Resection specimens of 3 cases of metaplastic thymoma were studied by light microscopy, immunohistechemistry and electron microscopy. Results All the 3 patients were females and aged 33, 58 and 45 years respectively. Histologically, a biphasic growth pattern, consisting of intimate admixture of epithelial ceils and spindle ceils, was noted. The epithelial ceils showed mild cytologic atypia, sometimes nuclear grooves and pseudonuclear cytoplasmic inclusions. These cells were arranged in nests and anastomosing cords. Mitotic figures were rarely seen. On the other hand, the spindle ceils were bland- looking, mitotically inactive and arranged in fascicles. Immunohistechemical study showed that the epithelial cells strongly expressed cytokeratin （AE1/AE3） but not vimentin or CDS. The proliferation index, as demonstrated by Ki-67 immunostaining, was about 3% to 5%. In contrast, the spindle ceils were diffusely positive for vimentin and epithelial membrane antigen. Staining for CD5 and CD20 was negative. The background lymphecytes were positive for CD3, but not for TdT and CD99. Ultrastructurally, well-formed desmesomes or hemidesmosemes were identified in the epithelial element. They were not detected within the spindle ceils. Conclusion Metaplastic thymoma is a rarely encountered indolent or low-grade thymic tumor and may represent a distinct clinicopathologic entity.