目的：探讨化生性胸腺瘤的临床及病理学特征。方法：应用光镜及免疫组织化学方法观察2例 化生性胸腺瘤的组织学特点及免疫学表型，并复习相关文献。结果：2例均为男性，年龄55岁及 56岁。组织学肿瘤显示双相分化特点，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 胞呈相互吻合的束状、岛状及宽大的梁状排列，细胞轻度异型，可见核沟及核内假包涵体，偶见核 分裂像；梭形细胞呈短束状或席纹状排列，细胞温和 ，未见核分裂像。免疫表型：上皮细胞区域 CK19和AE1/AE3呈强阳性表达，上皮膜抗原 (epithelial membrane antigen, EMA) 弱阳性；梭形细胞 区域表达Vimentin、Bcl-2及CD99，AE1/AE3局灶阳性，EMA弱阳性。两种区域中Ki67指数均<5%。 间质淋巴细胞CD3、CD5、CD20阳性，不表达TdT和CD99。结论：化生性胸腺瘤是一种罕见的良 性或低度恶性胸腺肿瘤，诊断依靠病理组织学和免疫组织化学标记，完整切除预后良好。
Clinicopathological analysis of metaplastic thymoma of two cases
Objective: To investigate the clinicopathologic characteristics of metaplastic thymoma. Methods: Two cases of metaplastic thymoma were studied histologically and immunohistochemically and the literatures were reviewed. Results: There were 2 male of patients with age of 55 and 56 respectively. Microscopically, all tumors were characterized by a biphasic pattern composed of epithelial components and spindle cells. The epithelial areas consisted of anastomosing cords and islands or broad trabeculae of cohesive neoplasia cells. Some epithelial cells showed mild cytologic atypia and the presence of prominent nuclear grooves or psedoinclusion, yet mitotic activity was very low. The cells were bland appearing with a fine nuclear chromatin pattern and mitoses were not found. Immunohistochemically, the epithelial cells were diffusely and strongly positive for CK19 and AE1/ AE3. The spindle cells were diffusely positive for Vimentin, BCl-2 and CD99. Two kinds of cells were focally and weakly positive for AE1/AE3 and epithelial membrane antigen (EMA). The Ki67 fraction was low (<5%) in both components. The scanty stromal small lymphocytes cells displayed a mature immunophenotype positive for CD3, CD5 and CD20 and negative for teminal deoxynucleotidyl transferase (TdT) and CD99. Conclusion: Metaplastic thymoma is a rare primary thymic epithelial tumor, and its biologic behavior is likely benign or lowly malignant process. The diagnosis of metaplastic thymoma mainly relies on its morphologic features and immunohistochemical profiles. Surgical excision alone is recommended.