原発性肺癌に合併し扁平上皮への分化を示した胸腺腫の1手術例 A Surgical Case of Thymoma with Squamous Differentiation Associated with Primary Lung Cancer

背景．今回われわれは原発性肺癌に合併し扁平上皮への分化という特殊な組織型を示した胸腺腫を経験したので報告する．症例．81歳男性．息切れ，胸痛を主訴に近医受診し，胸部X線にて左中肺野に結節影を指摘され，当院呼吸器内科紹介受診した．左B8aより経気管支吸引細胞診にてadenocarcinomaと診断され，手術目的に当科入院となった．肺癌の術前診断はcT1N0M0，stage IAであったが，術前の胸部CTにて前縦隔に径5.0×3.5 cm大の腫瘍を認め，胸腺腫が疑われ縦隔腫瘍摘出術も同時に行うこととした．手術は左肺下葉切除+リンパ節郭清（ND2a）および前縦隔腫瘍摘出術を施行した．術後病理診断では肺癌はadenocarcinoma，pT2N0M0，stage IBと診断した．また前縦隔腫瘍はtype B1 thymomaであり，その腫瘍細胞は角化を伴った扁平上皮への分化を示していた．結論．扁平上皮への分化を示す胸腺腫は特殊な病理組織像であり，胸腺腫と胸腺癌との関連を示唆する貴重な症例であると考えた．

Background. We report a case of thymoma with squamous differentiation associated with lung cancer. Case. An 81-year-old man consulted his family doctor with chief complaints of shortness of breath and chest pain. A nodular shadow was noted in the left middle lung field of his chest X-ray, and the patient was referred to our Department of Respiratory Medicine. Transbronchial aspiration cytology was performed in the left B8a, and the tumor was diagnosed as adenocarcinoma. He was then referred to our department for surgery. The preoperative diagnosis of the lung cancer was classified as cT1N0M0 and stage IA by preoperative evaluation. Another 5.0×3.5 cm tumor was detected in the anterior mediastinum in the preoperative chest CT, and a thymoma was suspected. Simultaneous left lower lobectomy with lymphadenectomy (ND2a) and surgical removal of the anterior mediastinal tumor were performed. The postoperative histological examination revealed the lung cancer to be adenocarcinoma, pT2N0M0 and stage IB. The anterior mediastinal tumor was type B1 thymoma, showing squamous differentiation with keratinization. Conclusion. Thymoma with squamous differentiation is a rare histopathological feature. This case was valuable in that it suggested a relationship between thymoma and thymic carcinoma.