2020 Volume 34 Issue 7 Pages 733-739
Metaplastic thymoma, adopted in the World Health Organization (WHO) classification in 2004, exhibits a biphasic architecture consisting of polygonal epithelial and spindle cells. Only about 30 cases have been reported so far. We report two rare cases of metaplastic thymoma. The first case was a 44-year-old woman presenting with bilateral ptosis, swallowing difficulty, severe fatigue, and a positive result for anti-acetylcholine receptor antibody (78.6 nmol/L). Computed tomography showed a well-circumscribed mass measuring 3.1 cm in maximum diameter in the anterior mediastinum. She was diagnosed with thymoma-associated myasthenia gravis, and underwent extended thymectomy through a median sternotomy. The second case was a 55-year-old man treated for prostate cancer. He underwent computed tomography for further examination. A well-circumscribed low-density mass was located in the anterior mediastinum. The anti-acetylcholine receptor antibody level was below 0.3 nmol/L. With a diagnosis of thymoma, he underwent thymectomy through a median sternotomy. In both cases, histology demonstrated the biphasic architecture of epithelial and spindle cells. The postoperative pathological diagnosis of both cases was metaplastic thymoma, pT1aN0M0 pStage I.
