Thymic carcinoma with myasthenia gravis: Two case reports

INTRODUCTION: Myasthenia gravis (MG) has been reported to correlate with earlier-stage thymoma, and theoretically does not accompany thymic carcinoma. However, we encountered two cases of thymic carcinoma with MG. PRESENTATION OF CASES: Case 1 involved a 54-year-old man who had been diagnosed with MG based on symptoms and detection of anti-acetylcholine receptor antibody (ARAB). Computed tomography (CT) revealed an anterior mediastinal tumor 30 mm in diameter. Prednisolone (PSL) and tacrolimus were administered without surgery at that time. Six years after diagnosis of MG, he was admitted to our hospital and underwent extended thymectomy. Pathological examination revealed type B2-B3 thymoma according to World Health Organization criteria, comprising 80% of the tumor with small cell carcinoma as 20%. Case 2 involved a 51-year-old woman. She had been diagnosed with MG based on eyelid ptosis and detection of ARAB. Ten years after diagnosis of MG, diaphragm elevation was detected on chest X-ray. CT revealed an anterior mediastinal tumor, 47 mm in diameter. We suspected tumor invasion to the right phrenic nerve, right atrium, and superior vena cava. We therefore performed extended thymectomy after preoperative radiotherapy (40 Gy). Pathological examination revealed squamous cell carcinoma. DISCUSSION: Most cases of thymic carcinomas appear to arise de novo, but appearance in thymomas has been described. In both our cases, MG was treated with pharmacotherapy alone without extended thymectomy, and thymic carcinoma was considered to have developed from the thymoma during long-term follow-up. CONCLUSION: Thymic carcinoma can accompany MG.