化生性胸腺腫の1例

Metaplastic Thymoma Underwent Surgery：Report of a Case

はじめに　化生性胸腺腫（metaplastic thymoma）は，組織学的に多角細胞成分と紡錘形細胞成分の二相性の増殖様式を示し，未熟なT細胞を認めないことを特徴とするまれな腫瘍である．化生性胸腺腫の1切除例を経験したので報告する．

Metaplastic thymoma is a rare histologic variant of thymic epithelial tumors and is characterized by a biphasic growth pattern. We herein report the case of 44-year-old woman who underwent surgery for metaplastic thymoma. Computed tomography scan revealed a well-circumscribed mediastinal tumor：56 mm in diameter with homogenous enhancement. The tumor was suspected to be a non-invasive thymoma, and thymomectomy with resection of the surrounding thymus was performed using thoracoscopy. The resected tumor measured 60 mm and was grossly well-encapsulated. The cut surface was gray to white and homogenous. Microscopically, the epithelial components took the form of an anastomosing nest to broad trabeculae intertwining with the bundle of spindle cells. Mitosis was not found and the Ki-67 index was ＜ 1％. Cytokeratin 5/6 was strongly positive in the epithelial components composed of polygonal cells. Terminal deoxynucleotidyl transferase positive immature T cells were not observed. Based on these pathologic findings, the tumor was identified as metaplastic thymoma.